FB/EK Holden Holley 350 Guide

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FB/EK HOLDEN

350 HOLLEY CARBURETTOR

ENTHUSIASTS GUIDE

REVISION DATE UPDATE

0 November 2011 Initial draft for review.

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Table of Contents

1 Background .................................................................................................................................................................... 3 2 Operation ....................................................................................................................................................................... 5

2.1 Fuel Inlet System ...................................................................................................................................................... 5

2.2 Idle System ............................................................................................................................................................... 6

2.3 Main Metering System............................................................................................................................................... 7

2.4 Accelerator Pump System ......................................................................................................................................... 8

2.5 Power Enrichment System ........................................................................................................................................ 8

2.6 Choke System ........................................................................................................................................................... 9

3 Capacity (CFM) ............................................................................................................................................................ 10

4 Mounting ...................................................................................................................................................................... 12

4.1 Manifolds ................................................................................................................................................................. 12

4.2 Adaptor Plates......................................................................................................................................................... 14

4.3 Accelerator Linkage to Cable Modification .............................................................................................................. 14

4.4 Fuel, Vacuum and Choke ........................................................................................................................................ 16

5 Factory Specifications .................................................................................................................................................. 20

6 Assembly Diagram ....................................................................................................................................................... 21

7 Channels and Passages .............................................................................................................................................. 23

7.1 Metering Block (Float Bowl Side) ............................................................................................................................ 23

7.2 Metering Block (Main Body Side) ............................................................................................................................ 23

7.3 Main Body (Metering Block Side) ............................................................................................................................ 24

7.4 Main Body (Throttle Body Side) ............................................................................................................................... 24

7.5 Main Body (Choke Horn Side) ................................................................................................................................. 25

7.6 Throttle Body (Main Body Side) ............................................................................................................................... 25

7.7 Throttle Body (Manifold Side) .................................................................................................................................. 26

8 Disassembly and Overhaul Process ............................................................................................................................ 28

8.1 Kit Contents and Pre-disassembly .......................................................................................................................... 28

8.2 Special Tools........................................................................................................................................................... 30

8.3 Removal and Disassembly ...................................................................................................................................... 30

8.4 Cleaning and Inspection .......................................................................................................................................... 34

8.5 Assembly ................................................................................................................................................................ 35

9 Tuning.......................................................................................................................................................................... 39

9.1 Fuel Level ............................................................................................................................................................... 39

9.2 Idle Speed and Idle Mixture ..................................................................................................................................... 41

9.3 Fast Idle Speed ....................................................................................................................................................... 43

9.5 Main Metering Jets .................................................................................................................................................. 47

9.6 Power Valves .......................................................................................................................................................... 49

9.7 Venturi Sleeves ....................................................................................................................................................... 51

10 Troubleshooting ...................................................................................................................................................... 53

11 Modification ............................................................................................................................................................. 54

11.1 Fuel Supply Stability ................................................................................................................................................ 54

11.1.1 Wedged Float ..................................................................................................................................................... 54

11.1.2 Float Bowl Vent Baffle (Whistle) ......................................................................................................................... 54

11.2 Higher Air Flow ........................................................................................................................................................ 55

11.2.1 Choke Horn Removal ......................................................................................................................................... 55

11.2.2 K&N Stubstack ................................................................................................................................................... 56

11.3 Automatic Choke ..................................................................................................................................................... 56

11.3.1 Automatic Choke Operation ................................................................................................................................ 56

11.3.2 Electric Choke Conversion ................................................................................................................................. 59

11.3.3 Hot Air Choke Conversion .................................................................................................................................. 61

11.3.4 Automatic Choke Tuning .................................................................................................................................... 62

11.4 Power Valve Blowout Preventer (Check Ball). ......................................................................................................... 64

11.5 Better Fuel Metering (Adjustable Metering Block) ................................................................................................... 64

12 Contacts .................................................................................................................................................................. 66

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1 Background

This document aims to provide some information regarding fitment of

350 Holley carburettors to FB and EK Holdens. It contains:

historical information, such as which jets and bleeds were originally fitted to 350 Holley carburettors,

practical information on identification, disassembly and reassembly of 350 Holley carburettors, and

guidance on tuning, replacement parts and overhaul techniques.

It contains answers to many of the questions that seem to come up

routinely on most of the early Holden forums:

“What jets should I run in my early Holden?”

“Why is my Holley carburettor running so poorly?”

“How do I set up a cable throttle?”

Whilst this document is primarily related to the FB and EK Holdens, much of the information is applicable

to other early Holdens. Please bear in mind that the 350 Holley carburettor was not an original fitment to

early Holdens, and hence that limited documentation is known to exist. Much of the information below is

drawn from internet forums, discussion with enthusiasts and common sense. I have used photos and

other information from a wide variety of sources, particularly from the forums – if anyone is offended by

my use of the material, feels I have breached copyright or needs recognition, please let me know and I

will correct the issue immediately.

I have drawn information from the following sources:

The Holley 2300 Handbook by Mike Ulrich (most notably the drawings used in Section 2),

Super Tuning and Modifying Holley Carburettors by Dave Emanuel,

Some very good info on how automatic chokes work and are tuned from

http://www.chevelles.com/techref/Adjusting_Automatic_Chokes.htm

Some info published online by Holley at www.holley.com.

Equally, I have made opinions and drawn conclusions on some of the information I have found and

equipment I have owned, and have cross-referenced some material - if anyone believes that I have made

an error (or knows a better way to do something), please let me know and I will update the document...

after all, the main purpose here is to help other early Holden enthusiasts. I have marked some text in red

in this document where I am missing information – any help in closing these gaps is appreciated.

Like all things automotive, installing, operating and maintaining a carburettor comes with a risk. Leaking

fuel lines can lead to fires, jammed throttles can lead to out-of-control vehicles and items dropped down a

carburettor throat can cause massive engine damage (amongst other hazards). Any advice contained in

this document is to be taken at the reader’s risk – qualified mechanics should be consulted where

appropriate.

The 350 Holley is a common choice for Holden inline six-cylinder engines. Whilst the carburettor is oversized for the original FB/EK Holden grey motor, it is a good match for the larger displacement red motors. 350 Holley carburettors are also mandated in some forms of racing. For example, the current specification for both Australian Speedway Production Sedan and Modified Production Sedan classes

http://www.chevelles.com/techref/Adjusting_Automatic_Chokes.htm

http://www.holley.com/

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mandates them for cars originally built in multiple carburettor or four-barrel carburettor form (though allows the venturi to be milled out from the stock 1

3/16” to 1

13/64”).

Having said that, Holley carburettors have a poor reputation amongst Holden owners. Some of the causes for this are:

Poor carburetor condition. Unfortunately, the average Holley has not been looked after too well, with a rebuild (either by a professional or by using a rebuild kit) strongly recommended,

Poor fuel atomisation, which can be resolved by installing venturi sleeves to increase fuel velocity, and

Poor fuel consumption, often caused by “over jetting” to try to hunt down the causes of the two issues above.

Each of the issues above will be tackled in this document. Holley has made a total of thirteen 350 CFM carburettors (all with 1

3/16” diameter venturis), as per the

table below:

List number Model

R3660 2300

R4055-1 2300

R4056-1 2300

R4144-1 2300

R4670 2300

R4791 2300

R4792 2300

R7448 2300

R80120 2305

R80320-1 2300

R80787-1 2300

R82010 2010

R87448 2300

However, most Holley 350 CFM

carburettors found on early Holdens are

List number R-7448, as per the image

to the right. I will focus on these

carburettors, and will refer to them as

“350 Holleys” for the remainder of the

document.

350 Holleys are a Model 2300 carburettor. Model 2300’s have been made by Holley since the mid 1950’s,

where they were used on Ford passenger car V8 engines. The 350 Holley is a non-staged two-barrel

carburettor (where the two barrels open at the same time by a common throttle shaft). 350 Holleys can be

identified by the List number, which is stamped onto the choke housing (see the red circle on the picture

above). Below the list number will be four digits (e.g. 1662). The first three digits are the day the

carburettor was manufactured (in this example the 166th day of the year) and the last digit is the year (2

for 1972).

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2 Operation

The 350 Holley carburettor has six basic systems that work together to provide the correct fuel/air mixture

over different engine loads:

• The fuel inlet system, which keeps a consistent level of liquid fuel “ready to go” in the carburettor,

• The idle system, which controls the fuel/air mixture at no-throttle and slight-throttle operation,

• The main metering system, which controls the fuel/air mixture at mid-throttle (or “cruise”) operation,

• The accelerating pump system, which adds a small “shot” of fuel when you initially put your foot down,

• The power enrichment system, which controls the fuel/air mixture at heavy throttle (hills, towing or

race) operation, and

• The choke system, which controls the air/fuel mixture for cold starting and warm-up.

Each of these systems will be described below.

2.1 Fuel Inlet System

The 350 Holley fuel inlet system consists of a fuel bowl, fuel inlet fitting, fuel inlet needle and seat, and a

float assembly. Fuel from the fuel tank is fed via the fuel pump to the carburettor. A sintered bronze filter

is usually installed in the fuel inlet fitting to capture dirt and rust and prevent them from blocking the fine

passages inside the carburettor. If the bronze filter (and associated spring and gasket) are omitted, an in-

line filter must be used. If the fuel

level is too low, the float (basically

a hollow brass or plastic ball that

floats on the fuel in the fuel bowl)

drops down and opens the fuel

inlet valve. This allows the

pressurised fuel to enter the

carburettor and begin filling the

float chamber. Once the fuel level

is high enough, the float rises, and

closes off the inlet valve. The float

chamber is vented by an internal

vent tube to the air horn. This

balanced pressure ensures that

fuel/air mixtures stay constant

even if the air filter is blocked by

dirt. The level of fuel in the float

chamber is adjusted by turning the

adjustment nut and lockscrew on

top of the float chamber (not shown in the simplified diagram). No disassembly is required to make this

adjustment, unlike the original factory Stromberg carburetors which required the air horn to be removed.

The fuel bowl on the 350 Holley carburettor is of the center-pivot type. This type of float is best for

speedway, gymkhana or road racing where fuel sloshing is from side-to-side (an aftermarket wedged-

shaped can also assist and will be discussed below). In drag racing applications, the front-to-back

sloshing of fuel (and lifting of the nose of the car) can cause this type of float to not operate as effectively.

A bumper spring under the hinge pin of the float helps to smooth out the float operation under stop/start

operation.

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Note that there are three types of float construction: hollow brass (left image below), solid black nitrophyl

(centre image below) and hollow white Duracon (right image below – the Duracon goes “pink” with use).

Brass floats are suitable for many different fuel types, but are unsuitable for blow-through forced induction

systems (as the increased pressure may crush the float) or where dual-fuel is used (as the LPG flowing

through the carburettor draws a substantive vacuum on the float bowl… and with the fuel inlet valve shut

that vacuum can easily crush the float). Solid nitrophyl floats are used when there is a risk of crushing,

though are not resistant to alcohol. Duracon floats are used as the factory-supplied float for new Holley

carburettors, and may be susceptible to both crushing and alcohol.

2.2 Idle System

Under very low engine speeds (idling), the engine does not produce enough vacuum to suck sufficient

fuel from the main metering system

(due to the near-closed throttle

plate). However, under the throttle

plate a high vacuum exists. This

vacuum is used to pull fuel from the

idle system. Fuel from the fuel bowl

enters the main wells through the

main metering jets that are screwed

into the metering block. Some of

this fuel is then bled off to an idle

well. The amount which is bled off

is limited by the idle feed restriction.

The idle fuel is then mixed with air

from the idle air bleed hole. The

idle air bleed hole also determines

when the idle system starts flowing

fuel – the larger the idle air bleed,

the slower the idle system is to start

flowing. The air/fuel mixture then

passes to the idle discharge port

below the throttle plate where it is

discharged, as per the diagram to

the right. Idle mixture screws are located on the sides of the primary metering block. These control the

volume of the pre-mixed air/fuel coming through the idle well. Turning the screws clockwise (in) will “lean”

the idle system, whilst turning the screws counterclockwise (out) will “richen” the idle system. This part of

the idle system is often referred to as “curb idle".

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The idle system also has a branch

that delivers air/fuel mixture to a

transfer slot above the throttle

plate. When the throttle is closed

(curb idle), there is little vacuum

above the throttle plate, and the

transfer slot does not flow. As the

throttle begins to open, the

transfer slot is uncovered, and

vacuum draws fuel from it, as per

the diagram to the left (the

diagram looks like a second idle

discharge hole, but it really is a

vertical slot). The transfer slot

provides fuel supply for the

transition between curb idle and

cruise (when the main metering

jets take over). The more the

throttle plate opens, the more of

the transfer slot is exposed to

vacuum, and the more fuel flows

through the slot. Note that the

fuel/air mixture flowing to the transfer slot is not altered by the idle mixture screws – the idle mixture

screws only adjust the curb idle mixture.

2.3 Main Metering System

The main metering system is

designed to supply the leanest fuel

mixture for cruising in the 35mph

(60km/h) and over range. Fuel

from the float bowl passes through

the main metering jets and enters

the main well. Here it is mixed with

air from the main air bleed. The air

emulsifies the fuel to allow easier

vapourisation, and lowers the

mixture viscosity for earlier feeding

of the main metering system. The

main air bleed hole also

determines when the main

metering system starts flowing fuel

– the larger the main air bleed, the

slower the main metering system

is to start flowing. Engine vacuum

pulls this air/fuel mixture and discharges it through the booster venturi. The booster venturi is located just

above the main venturi, and acts amplify the vacuum applied to the main metering and power enrichment

systems.

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2.4 Accelerator Pump System

The accelerator pump system injects a small amount of fuel into the carburettor throat when the throttle is

opened. The system provides

good throttle response (sharp

acceleration). When the throttle

turns, a pump cam acts against a

series of levers to move the pump

diaphragm. The pump cam profile

determines how fast and how

much fuel is injected for each

degree of throttle shaft rotation.

The pump diaphragm moves

upwards, closing the pump inlet

check valve and opening the

discharge check valve. Fuel is

forced through a discharge nozzle

and into the carburettor throat,

hitting the outside of the booster

venturi. When the throttle is

released, the diaphragm moves

back downwards under pressure

of the return spring. The

discharge check valve shuts, the pump inlet check valve opens and fuel is drawn from the float bowl to

refill the pump, ready for the next “shot”.

2.5 Power Enrichment System

When running under heavy load

(high speed, towing, travelling up

hills or racing), a richer mixture is

required, which is supplied by the

power enrichment system. 350

Holley carburetors utilize a

vacuum operated power

enrichment system. Manifold

vacuum is connected to the power

valve and holds the power valve

piston shut. Under heavy load, the

manifold vacuum decreases.

When the manifold vacuum is low

enough, it can no longer hold the

power valve piston shut. The

opening power valve supplies

extra fuel through the power valve

channel restriction to the main

metering system.

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The vacuum level at which the valve opens can be tuned by selecting different power valves.

2.6 Choke System

When starting a cold engine, a

richer than normal mixture is

required (because the slowly-

spinning engine produces little

vacuum to draw out fuel, and much

of the fuel condenses on the cold

inlet manifold walls). To do this, the

choke valve is shut, restricting air

into the carburettor. 350 Holley

carburettors are fitted with manual

chokes. A bowden cable operates

the choke linkage, opening and

closing the choke plate. The choke

linkage also incorporates a fast idle

cam. The fast idle cam bumps

open the throttle a small amount

when the choke is opened,

increasing engine speed. The

choke plate is offset and spring

loaded, such that the plate opens

slightly as the airflow increases

(leaning the mixture).

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3 Capacity (CFM)

There are some engine combinations where the original single-barrel Stromberg carburettor becomes

restrictive. It is common practice for enthusiasts to go hunting for a larger carburettor in the search for

more power… and sometimes that hunt finishes with a 350 Holley carburettor. Carburettors are often

rated in terms of the amount of fuel/air mixture they can flow at a given manifold vacuum. The flow rate is

expressed in cubic feet per minute, or CFM. Care needs to be taken though in that a given carburettor

may have several different venturi sizes, and hence several different flowrates (for example the BXUV-2

carburettor was offered in both 1/32” and

3/32” venturi sizes for early Holdens). The manifold vacuum used

to measure flow rate also varies. Some early published ratings for 1-barrel (e.g. B–Model Stromberg) and

2-barrel (e.g. WW-Model Stromberg and 350 Holley) carburetors were measured at 3” Hg. 4-barrel

carburettors (for example Holley 4150 carburettors) were rated at 1½”Hg. This means that a 600CFM 2-

barrel does not flow the same as a 600CFM 4-barrel – the 4-barrel flows 40% more as it is tested at

higher pressure drop.

The table below has been compiled from information on multiple websites. I have converted the

Quadrajet, Weber, and SU values to 3”Hg (they were published at 1.5”Hg). I have taken a single

published figure for Stromberg BXOV-2 carburetors (210CFM) and converted to the smaller BXOV-1 and

BXUV-2 carburettors by calculation based on the venturi and throttle bore diameters. The upshot of the

above is that the table below is very approximate, but should give some indication of the relative flowrate

achievable with different carburettors.

Carburettor Barrels Venturi diameter Flowrate (CFM @3”Hg)

Weber 38-DGAS 2 36mm/36mm 600

Rochester Quadrajet 4 2¼ “/1.35” 530

Mikuni 44 PHH 2 37mm/30mm choke 422

Holley 7448 (“350 Holley”) 2 13/16”/1

3/16” 350

SU HIF6 1 Variable 339

Weber 28/36-DCD 2 26mm/27mm 317

SU HS6 1 Variable 297

Stromberg BOV-2 (the “big brother swap”)

1 19/32” 287

WW Stromberg 2 128

/32”/ 128

/32” 280

Weber 32/34-DMTL 2 26mm/27mm 274

Weber 32/36-DGV 2 26mm/27mm 270

Weber 32/36-DGV 2 23mm/27mm 235

Stromberg BXV-2 1 15/32” 210

Stromberg BXUV-2 1 13/32” 201

SU HS4 1 Variable 201

SU H4 1 Variable 188

Holley EGC 2 11/16”/ 1

1/16” 185

Stromberg 48 2 11/32”/1

1/32” 175

Stromberg BXOV-1 1 13/32” 162

Holley 94/8ba 2 15

/16”/ 15

/16” 162

Stromberg LZ 2 1”/1” 160

SU H2 1 Variable 156

Holley 94/59 2 15

/16”/ 15

/16” 155

Stromberg 97 2 31

/32”/ 31

/32” 150

Holley 92 2 7/8”/

7/8” 142

Stromberg 81 2 13

/16”/ 13

/16” 135

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Note that the chart below indicates the required carburettor capacity for typical early Holdens (around

80% volumetric efficiency). The blue line shows that a 350 Holley has sufficient capacity for even a 202ci

motor running at 7500RPM.

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4 Mounting

4.1 Manifolds

A number of manifolds are available to mount 350 Holley carburettors to early Holden motors. One of the most common manifolds used for early Holdens is the Redline Performance Torker II 2V manifold (part number 12-65M – see image to the right). This is a multi-fit manifold that can be used on 149-202 red motors and 2.85 or 3.3 blue motors.

Redline Performance also produced a Roadmaster manifold (see image to the right). John Cain produced similar style manifolds for fitting 350 Holley carburettors to Holden red motors (see image to the right). AussieSpeed

® once

manufactured Cain Manifolds, though the name was later dropped from their product line. Lynx made a number of manifolds for fitting 350 Holley carburettors to Holden red motors, both in a style similar to the Redline and Cain manifolds (see image to the right), and in a long-runner format (see image to the far right. Unfortunately, Lynx are no longer producing manifolds. Firestreak made a water-heated manifold for 350 Holley carburettors. A manifold was also produced with SS cast into it.

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Manifolds for fitting 350 Holley carburettors to early Holdens are also made by AussieSpeed®. In 2009,

negotiations started with Kit Cullan to buy the Holden 6 cylinder Cullan Special manifolds to suit red and blue motor 6 cylinder engines. After testing and looking at the changes and benefits in the newer style of inlet manifolds AussieSpeed

® had been working on, the Ultraflow pattern equipment underwent massive

modifications and the Ultraflow name is no longer used. The following manifolds were made by AussieSpeed

®, but are no longer in production:

AussieSpeed

® part number AS0001 Holden 9-port 149-202 red motor.

This manifold will work on a standard engine. Street and competition manifold with tall plenum, plenum divider, long sweeping runners for wider rev range, this is a smaller runner designed for maximum air speed, good torque and fast acceleration. AussieSpeed

® part number AS0266 Cullen Special (Kit Cullan)

Ultraflow Holden 9-port 179-202 and 208/218 stroker engines. The corresponsinf 12-port manifold is part number AS0267. The current AussieSpeed

® manifold for red motor 9-port manifolds is part number AS0167 (below left)

and AS0169 for 12-port heads. The design offers high port velocity and a divided plenum that feeds all runners equally.

http://www.aussiespeed.com/components/com_virtuemart/shop_image/product/Holden_red_motor_4bdea42a88d50.jpg

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4.2 Adaptor Plates

Whilst not ideal, it is also possible to reuse the factory inlet manifold, using an adaptor plate to mount the Holley carburetor flange (see dimensions below for various early Holden flanges).

350 Holley Bendix Stromberg BX-Model Bendix Stromberg WW-Model The factory single-barrel Holden Stromberg manifolds are able to be used with an adaptor plate (e.g. Redline Performance part No. 10-501 for 149-186 engines, 10-502 for 202 or, 10-503 for late 202). Whilst operable, this setup has poor airflow, reducing performance. They suffer from fuel cone breakup which will allow the fuel to fallout and puddle rather than moving smoothly through the intake system. WW Stromberg manifolds are able to be used with a similar adaptor plate (e.g. Redline Performance part No. 10-187 or 10-233). The open nature of this plate has a far less disruptive effect on fuel flow.

For Varajet II manifolds, an adaptor plate is also available (e.g Redline Performance part Nº. 10-219). Varajet carburetors were found on WB Holden 202, UC Torana 1.9L, VC and VH Commodore 1.9L, 2.85 and 3.3L, and some VK Commodore 3.3L engines (some VK Commodores had Bosch LEII-Jetronic fuel-injection).

4.3 Accelerator Linkage to Cable Modification

With some carburettor manifolds and linkages, it is possible to use the original FB/EK Holden throttle

linkage (the swinging bar type) with a little bending. However, the 350 Holley carburettor is generally

operated by converting the throttle linkage to a cable type, eliminating the complex linkage. A number of

pedal/cable assemblies can be mounted into FB/EK Holdens, notably HZ Holden and Commodore.

A neat (and simple) solution is to retain the

original FB/EK pedal, and modify it to suit the

cable from a Mitsubishi L300 Express van.

These vehicles were sold from 1980-1986,

and look similar to the photographs to the

right. Note that the later models however do

not have the required clevis at the cable end.

http://www.redlineauto.com.au/products/product/10-187?category=GQGRYXUE&

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The Mitsubishi L300 accelerator cable is quite long, and can be shortened with a simple pair of

sidecutters to the correct length once installed.

To undertake the conversion:

1. Remove all the throttle linkage except the pedal.

Remove the clip connecting the lower cross shaft operating rod to the accelerator pedal (under the

car),

Unbolt the lower cross shaft assembly (four phillips-head bolts located under the car).

Remove the clip connecting the upper cross shaft operating rod to the upper cross shaft assembly.

All the linkage from under the car should now fall out

Unbolt the upper cross shaft support (two phillips-head bolts per bracket, one bracket on drivers

and passengers side of firewall.

Disconnect the throttle control upper rod from the carburettor. All the linkage from in the engine bay

should now fall out.

Don’t discard all the parts yet – the upper cross shaft support from the passenger’s side makes a good

bracket for supporting the cable later.

2. Attach the Mitsubishi L300 accelerator cable clevis to the original Holden accelerator pedal, using the

hole that the lower cross shaft operating rod mounted to (under the car). The cable can be attached

with a pin and split pin, or by using a small bolt and nylock nut (do not overtighten the nut as it will bind

the clevis).

3. The cable will now run into the cabin using the Mitsubishi L300 cable guide. You will need to drill a

hole in the floorpan for the cable to pass through, and another two for the cable guide mounting bolts.

Mount the cable guide using nuts, bolts and spring washers, with some sealant under the cable guide

to prevent water ingress to the cabin. The photographs above show the mounting of the clevis and

cable guide on a number of vehicles.

4. Run the cable inside the cabin, up the firewall (under the carpet/floor mat) and pass it out through the

grommet where the original choke cable passes through. The picture to the right

shows the cable routing with the carpet/floor mat removed.

5. The cable then passes across the engine bay to the carburettor throttle linkage. The

cable must be mounted, similarly to the way that the choke tube holder assembly

mounts the original choke cable (the photograph below to the right shows a holder

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assembly fitted to a Holley carburettor, and the photograph to the left to a twin Stromberg setup).

6. The cable setup often feels much lighter than the original throttle linkage, and an extra (or heavier)

return spring can assist in returning the pedal feel. The photo below to the right shows a return spring

mounted off a bracket on the original battery tray.

7. The cable assembly should be checked and adjusted so that the carburettor both achieves wide open

throttle, and returns to idle. It’s a good idea not to cut the cable to final length until this has been done.

In some cases, it may be necessary to extend the accelerator pedal lever (by welding on a piece of flat

bar) in order to get enough pedal travel to attain full throttle.

4.4 Fuel, Vacuum and Choke

The fuel connection at the inlet of the Holley 350 carburettor is located at a similar position to the original Stromberg carburetor for FB/EK Holdens. Provided the manifold chosen does not have long runners, it is possible with some gentle bending to get the original fuel line to align with the carburettor. The Holley carburettor inlet is AN-5 (SAE thread size ½-20) thread, as is the original FB/EK fuel inlet line. Note that the recommended fuel pressure for 350 Holley carburettors is 5-7 psi. Whilst standard GMH grey/red/blue motor fuel pumps (at 3.9 - 4½ psi) are adequate, care must be taken when an electric fuel pump has been added – the higher than required fuel pressure forces open the needle and seat, flooding the engine. The chart and table below provide some guidance. When using inline fuel pumps (notably Holley), a pressure regulator is mandatory to prevent flooding.

Fuel Pump Maximum Pressure (psi) Free Flow (GPH) Facet SS208 3½ 14

Facet SS171 3½ 14

Later Holden (blue motor steel can) 3.9 9½

Facet SS500 4 25

Facet 60104 4 25

Facet IP002 4 32

Early Holden (grey/red glass bowl) 4½ 9

Facet SS148 4½ 24

Facet SS501 4½ 30

Facet SS165 5 15

Carter GP4600HP 5 100

Facet STS504 5½ 30

Facet IP007 5½ 36

Facet IP131 5½ 36

Facet IP220 5½ 36

Facet 60106 6 32

Facet SS135 6 34

Carter GP4603HD 6 43

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Carter GP4070 6 72

Facet SS502 7 32

Facet STC505 7 35

Facet IP051 8 30

Facet RTW506 8 40

Facet BTP001 8 40

Facet BTP001 8 40

Carter GP4594, GP4389, GP4259 and GP4602RV 8 72

Facet SS200 9 32

Facet SS503 10 34

Facet 60107 10 34

Holley Red 10 100

Facet SS185 11½ 29

Facet 40222 11½ 33

Facet 40223 11½ 33

Facet 40237 11½ 33

Carter GP4601HP 18 100

Holley Blue 18 110

Holley Black 18 145

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0

20

40

60

80

100

120

140

160

0 2 4 6 8 10 12 14 16 18

Flo

w (

GP

H)

Prressure (psi)

Holley red

Holley blue

Holley black

Stromberg inlet pressure

350 Holley inlet pressure

early Holden fuel demand

Pressure regulator required to drop Holley red pressure down to 350 Holley 3-7psi inlet pressure range.

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Increasing fuel pressure will also require the fuel level in the carburettor to be reset – as a rule of thumb, every one psi of fuel pressure increase will raise the fuel level

1/32”.

The 350 Holley carburettor has a number of vacuum sources:

full manifold vacuum, a 3/8” pipe located behind the throttle body provides vacuum for power brakes,

vacuum windshield washers and PCV valves (if you have more than one of these, you will need to use plastic vacuum tees from an automotive parts store like SuperCheap or Repco). Full manifold vacuum is tapped off from below the throttle plates. You get more manifold vacuum when you take your foot off the throttle (this is why pre-EK vacuum wipers work so well when you lift your foot, but run poorly when you have your boot into it driving uphill in the pouring rain!).

timed spark vacuum, a 3/16” pipe located in the choke side of the primary metering block. Timed-spark

vacuum (sometimes referred to as distributor vacuum) is taken from above the throttle plates. Timed spark vacuum is exactly the same as manifold vacuum – except that it is shut off under zero throttle (i.e. under idle conditions, there is huge manifold vacuum, but zero distributor vacuum). The strategy behind distributor vacuum (generally used in later-model carburettors) is to remove vacuum advance at idle, causing the vehicle to run hotter and combust exhaust emissions (often with the help of air injection systems at the exhaust manifold).

Early Holdens were designed to run timed spark vacuum (the vacuum port connection is at the throttle body above the throttle plate – see diagram to the right). There is no harm in running distributor vacuum. However, for cars with large cams (high valve overlap and poor vacuum), tapping into manifold vacuum (and blocking off the distributor vacuum ports on both the carburettors) can give better vacuum signal at idle, more advance and hence better idling. This can also reduce engine temperature at idle. Note that the original FB/EK vacuum line ends in a

1/8” NPT thread nipple (the nut is

7/16” AF). If using the full

manifold connection, rubber vacuum hose can be clamped over both the original nipple and the 350 Holley manifold vacuum pipe. If the timed spark vacuum connection is used, it may be necessary to cut off the original nipple and use smaller diameter rubber vacuum hose to clamp to the (cleaned and smoothed) pipe end. Cap-off any vacuum source that is not used (plastic vacuum caps are available from automotive spare parts stores like SuperCheap and Repco from the same carousel that sells small blister packs of nuts and bolts). 350 Holley carburettors were originally fitted with manual chokes, which will connect directly to the original FB/EK choke cable.

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5 Factory Specifications

The following table lists the factory (“out of the box”) specifications for the List number 7448 350 Holley

carburettor:

Model number 2300, List number 7448.

350CFM (@ 3”Hg) capacity. Intended as stock performance replacement for 2-barrel street applications. Also mandated carburettor for some oval track racing sanctioning bodies.

Venturi diameter 13/16” (main body part number 6R1919).

throttle bore 1½” (throttle body part number 12R-5174B, also stamped 7448 underneath). Throttle plates stamped 107. Throttle bore and shaft assembly part number 12R11070A.

Manual choke.

30cc accelerator pump (accelerator pump cover part number 34R2178B) with “Orange” accelerator pump cam (part number 41R466) in position #2. Tube type discharge nozzle size 0.031” (part number 121-31).

Viton® tipped adjustable needle with 0.110" seat (part number 6-504).

#60 main metering jets with ¼-32 UNF thread (part number 122-61).

Fuel bowl part number 134-103 (marked 36R4649B), with fuel bowl gasket part number 108-83-2. Centre hung float part number 116-2. Fuel inlet fitting tapped to AN-5 (SAE thread size ½-20) to suit 5/16” OD tube.

Metering block part number 134-203 with metering block gasket part number 108-89-2. Metering blocks stamped L7448

Single stage normal flow power valve opening at 8.5”Hg (part number 125-85). Power valve channel restriction approximately 0.056”.

One 3/16” timed-spark vacuum port (tapped from left side of metering block) and one

3/8” manifold

vacuum port (tapped from rear of throttle body). Choke vacuum port (for fitment of hot-air or electric choke) controlled by a 0.055” (#54 drill) orifice screwed into the base of the throttle body.

Ford automatic transmission kickdown, does not work with automatic overdrive transmissions.

Renew Kit part number 37-1536, Trick Kit part number 37-933, Fast Kit part number 37-1543.

WARNING: If you are using this carburetor with a GM overdrive transmission TH700R4 or a TH200R4, you must use a transmission kickdown cable bracket (Holley P/N 20-95) and stud (Holley part number 20-40). Otherwise, SEVERE transmission damage WILL result. This carburetor is not designed to work with ANY other automatic overdrive transmission.

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6 Assembly Diagram

Holley provides a generic assembly diagram for Model 2300 carburettors at

http://www.holley.com/data/TechService/Technical/2300%20Exploded%20View.pdf, and for Model

2300 carburettors set up for 3x2 configuration at

http://www.holley.com/data/TechService/Technical/2300%20(3x2)%20Exploded%20View.pdf.

However, neither diagram maps out the 350 Holley carburettor very simply – both diagrams are generic,

and have either extra or missing parts. I have taken both these diagrams and “cut and shut” them to

make the 350 Holley assembly diagram below.

http://www.holley.com/data/TechService/Technical/2300%20Exploded%20View.pdf

http://www.holley.com/data/TechService/Technical/2300%20(3x2)%20Exploded%20View.pdf

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No Description No Description No Description

1 Fuel bowl screw (4 off) 29 Metering body 57 Back-up plate stud nut

lockwasher

2 Bowl screw gasket (4 of) 30 Metering body gasket 58 Stud nut

3 Fuel inlet fitting 31 Power valve gasket 59 Throttle body

4 Inlet filter gasket 32 Power valve 60 Pump cam lock screw

5 Inlet filter screen 33 Throttle body gasket 61 Pump cam

6 Inlet filter spring 34 Main body 62 Curb idle screw spring

7 Inlet fitting gasket 35 Pump discharge nozzle

screw 63 Curb idle screw

8 Fuel inlet check plug 36 Discharge nozzle gasket 64 Throttle shaft bearing

9 Check plug gasket 37 Pump discharge nozzle 65 Throttle shaft centre bearing

10 Accelerator pump cover

screw (4 off) 38 Discharge nozzle gasket 66 Throttle shaft bearing

11 Accelerator pump cover 39 Pump discharge check valve 67 Fast idle cam lever screw

12 Pump diaphragm 40 Choke plate screw (2 off) 68 Fast idle pick-up lever

13 Diaphragm return spring 41 Choke plate 69 Fast idle cam lever spring

14 Float lever shaft 42 Choke shaft and lever 70 Fast idle cam lever

15 Float assembly 43 Choke link seal 71 Throttle plate screw

16 Float spring 44 Choke link 72 Throttle plate (2 off)

17 Float shaft retainer 45 Control lever nut 73 Fast idle cam lever spring

18 Fuel valve seat lockscrew 46 Lockwasher 74 Fast idle cam lever screw

19 Lockscrew gasket 47 Choke lever and swivel

assembly 75

Throttle body to main body screw (5 off)

20 Fuel valve seat adjustment

nut 48 Swivel screw 76 Choke vacuum supply orifice

21 Adjustment nut gasket 49 Fast idle cam plate 77 Pump operating lever

adjustment nut

22 Fuel valve assembly 50 Plunger spring 78 Pump operating lever

adjustment spring

23 Fuel bowl gasket 51 Fast idle cam plunger 79 Pump operating lever

adjustment screw

24 Fuel bowl assembly 52 Fast idle cam and shaft

assembly 80 Pump operating lever

25 Metering body gasket 53 Back-up plate and stud

assembly 81

Pump operating lever retainer

26 Idle needle (2 off) 54 Choke rod lever and bushing

assembly 82 Throttle shaft and lever

27 Idle needle seal (2 off) 55 Choke spring 83 Throttle return spring

28 Main metering jet (2 off) 56 Spring washer 84 Choke housing screw (3 off)

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7 Channels and Passages

The images below illustrate the channels and passages cast and machined into the 350 Holley

carburettor.

7.1 Metering Block (Float Bowl Side)

1. locating dowels

2. float bowl vent from float bowl to main body

3. accelerator pump discharge from float

bowl

4. main metering jet mounting holes

5. timed-spark vacuum port

6. power valve mounting hole

7. accelerator pump transfer passage

from fuel bowl to main body

8. curb idle fuel passage from needle

valve to main body

9. idle well

10. timed-spark vacuum passage

11. main well

12. gasket sealing bead

7.2 Metering Block (Main Body Side)

1. locating dowels


3. curb idle discharge from needle valve to main body

4. idle transfer fuel to main body

5. timed-spark vacuum port

6. power valve mounting hole

7. accelerator pump transfer passage

from fuel bowl to main body

8. air bleed from main body to main

well (approximately 0.0385”

diameter)

9. air bleed from main body to main

well (approximately 0.027”

diameter)

10. timed spark vacuum port to nipple

11. idle feed to idle well

12. idle bleed air from main body

13. idle down well

14. main air well

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15. power valve channel restriction (approximately 0.056” diameter)

16. idle fuel from main well

17. main fuel passage from main well to main body

18. timed-spark vacuum passage

19. gasket sealing beads

7.3 Main Body (Metering Block Side)

1. fuel from accelerator pump to pump discharge nozzle

2. air from idle air bleed to metering block

3. fuel emulsion to main discharge nozzle

4. air from main air bleed to metering block


6. vacuum from above throttle plate to timed-

spark port

7. fuel emulsion to curb idle discharge hole

8. fuel emulsion to idle transfer slot

9. locating dowels

10. fuel bowl vent to air cleaner

11. fuel bowl/metering body/main body mounting

holes

12. air from idle air bleed to metering block

13. not used (blanked hole)

14. power valve vacuum chamber

15. manifold vacuum from under throttle plates to

power valve vacuum chamber

7.4 Main Body (Throttle Body Side)

1. throttle body to main body mounting holes

2. choke vacuum supply for hot air and electric

chokes

3. idle fuel emulsion to idle discharge hole below

throttle plate

4. transfer idle fuel emulsion to transfer slot

above throttle plates

5. timed-spark vacuum connection to hole above

throttle plate on one barrel only

6. manifold vacuum from under throttle plates to

power valve

7. not used – blind channel

8. booster venturi

9. not used – blind hole

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10. not used – hole through to airhorn, but no hole in throttle plate or throttle plate gasket

7.5 Main Body (Choke Horn Side)

1. unused (blind holes)

2. air cleaner stud mounting hole

3. fuel bowl vent tube

4. venturi

5. booster venturi

6. unused (blind hole)

7. idle air bleed (approximately

0.035” diameter)

8. main air bleed (approximately

0.0775” (5/64”) diameter)

9. not used (blind holes)

10. fuel from accelerator pump to

pump discharge nozzle

7.6 Throttle Body (Main Body Side)

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2. transfer idle fuel emulsion to transfer slot above throttle plates

3. idle fuel emulsion to idle discharge hole below throttle plates

4. timed-spark vacuum connection to hole above throttle plate on one barrel only

5. unused (blind hole)

6. manifold vacuum from under throttle plates to power valve

7. choke vacuum supply for hot air and electric chokes

8. manifold vacuum port

9. mounting holes for brackets (e.g. dashpot)

7.7 Throttle Body (Manifold Side)


2. choke vacuum supply for hot air and electric chokes

3. manifold vacuum from manifold to nipple

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4. manifold vacuum from under throttle plates to power valve

5. mounting holes for brackets (e.g. throttle linkage or dashpot)

6. unused hole

7. mounting holes for brackets (e.g. throttle linkage or dashpot)

8. manifold vacuum port

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8 Disassembly and Overhaul Process

The following process describes the process of removal, disassembly and overhaul (often referred to as

“putting a kit through”) for a 350 Holley carburettor.

8.1 Kit Contents and Pre-disassembly

The 350 Holley carburettor overhaul illustrated below will be completed with a

genuine Holley Fast Kit, part number 37-1543. Suits R4412, 4412-1, 4412-2, 4412-3,

7448, 9647, 84412, 87448. The kit contains the following parts:

1. Metering body gasket

– see note 1.

2. Fuel bowl gasket –

see note 2.

3. Correct flange gasket.

4. Incorrect flange

gasket (not used for

overhaul of 350

Holley carburettors).

5. Paper gasket to seal

choke air supply.

6. Four plastic bowl

screw gaskets.

7. Rubber umbrella inlet

(not used for overhaul

of all 350 Holley

carburettors).

8. Two cork idle needle

seals.

9. Incorrect throttle body

gasket (not used for

overhaul of 350

Holley carburettors).

10. Correct throttle body

gasket.

11. Incorrect 50cc accelerator pump diaphragm (not used for overhaul of 350 Holley carburettors).

12. Correct 30cc accelerator pump diaphragm.

13. Fuel filter.

14. No. 65 power valve – see note 3.

15. Fuel valve assembly.

16. Inlet fitting gasket.

17. Power valve gasket – see note 4.

18. Fuel filter gasket.

19. Adjustment nut gasket.

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20. Check plug gasket.

21. Lock screw gasket.

22. Pump discharge screw gasket.

Plus two sheets of paper instructions.

Note 1: the metering body gasket supplied in the kit is slightly

different to the original Holley part. One hole is not stamped in

the kit gasket (see red circle on the image to the right).

However, this hole is not used in 350 Holley carburettors, and

the kit gasket is acceptable to use.

Note that 350 Holley carburettors use no

accelerator pump transfer tube. This

means that the gasket on the left (set up

for an accelerator pump transfer hole),

as supplied in the kit, must be used. Use

of a gasket like the one on the right will

lead to internal leaks and poor

operation.

Note 2: the fuel bowl gasket supplied in the kit has two

accelerator pump passages (the gasket is symmetrical). Some

gaskets however only have one passage (see image to the

right), and care must be taken that the gasket is put on the right

way around – otherwise the gasket will cover the accelerator

pump, and no pump shot will occur on acceleration.

Note 3: the factory 350 Holley power valve opens at 8.5”Hg

(often referred to as an “85” power valve). The kit above

(and most kits nowadays) supplies a valve that opens at

6.5”Hg (a “65 power valve). Power valves may be identified

either from the opening setting being stamped into one of

the valve nut flats, or onto the valve head as seen in the

image to the right (which shows a 65 power valve).

Note 4: two different power valves are available for 350 Holley carburettors.

The first (labeled “A” in the image to the right) has drilled holes in the valve,

and a tanged gasket. The second (labeled “B” in the image to the right) has

square “window” holes in the valve, and uses a circular gasket. The kit above

(and most kits nowadays) uses the second type. Care must be taken to use

the correct gaskets with the correct type power valve to avoid leakage.

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Prior to disassembling the carburettor, it is worthwhile checking for worn throttle shaft bearing areas. To

do so, start the engine and leave it idling with the air cleaner in place. Spray some WD40 around the

throttle body where the throttle shaft assembly passes through either side, using the red squirty straw on

the can of WD40 to get at the right area. Make sure there is no grease or dirt around the area that could

block the WD40 from getting to the throttle body. If the engine revs pick up, then the throttle shaft bearing

areas are worn (letting in WD40 under vacuum to fuel the motor) and should be professionally rebushed

during the rebuild.

8.2 Special Tools

Most of the overhaul process can be undertaken with basic garage tools – screwdrivers, long nosed

pliars, a set of imperial spanners and a 1” socket or spanner, a gasket scraper, some imperial drill bits

and a set of feeler gauges. Whilst they are not critical, if you are overhauling a few Holley carburettors it is

worthwhile buying a set of imperial feeler gauges and “narrow and bending” the 0.011”, 0.015” and 0.020”

gauges – more on these below. A torque wrench calibrated in inch-pounds (not foot-pounds!) is also

useful (not critical), though needs a slot-head screwdriver fitting (they are also useful for adjusting

automatic transmission bands during servicing if you need an excuse to buy one).

8.3 Removal and Disassembly

1. Remove the air filter, taking care not to drop the stud nut down the carburettor throat.

2. Allow the engine to cool prior to disconnecting the fuel line at the carburettor fitting. Note that the fuel

line may be under pressure from the fuel pump, and can leak some fuel – some rags to mop the fuel

up or a steel drift to plug rubber fuel lines are useful.

3. Disconnect the manifold vacuum hose at the rear of the throttle body base, and the timed spark

vacuum hose at the side of the metering block. Plug off the disconnected hoses. Note that in some

cases either or both of these hose connections may be not used, and may hence be capped off at

the carburettor with plastic caps.

4. Loosen the choke cable holder and swivel screw and disconnect the choke cable.

5. Remove any throttle return spring(s) fitted. Loosen any throttle cable clamp fitted then disconnect the

throttle cable (a throttle stud is often used).

6. Undo the four carburettor to manifold nuts and remove them, taking care not to drop them down the

carburettor throat. Lift the carburettor off the manifold studs, taking care not to bump any dirt down

the manifold. Remove the manifold gasket then cover the manifold opening with clean rag.

7. Undo the two slot-head screws and remove the choke cable holder bracket. Undo the remaining slot-

head screw and remove the choke lever and swivel assembly, fast idle cam plate and fast idle cam

and shaft assembly as one unit.

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8. Remove the choke link

hairpin clip then remove the

back-up plate and stud

assembly, choke rod lever

and bushing assembly and

choke spring as one unit.

Remove the paper gasket

covering the choke vacuum

passage (see red arrow on

image to the right). Some carburetors have this passage filled with a lead ball – if a lead ball is

present, do not disturb it.

9. Turn the carburettor over and undo the phillips-head fast idle

cam lever screw. Remove the fast idle pick-up lever, fast idle

cam lever spring and fast idle cam lever as one unit.

10. Undo the 11

/32”

control lever and

back-up plate stud

nuts, and unscrew

the slot head fast

idle cam lever

screw.

Dissassemble the

choke assemblies

Note that the choke link and choke link seal are not removed from the airhorn. To do so requires removal

of the choke plate. This is quite an involved process (filing off the choke plate screws and restaking them

on reassembly), and not generally needed for an overhaul.

11. To support the carburettor and prevent damage to the throttle

plates/throttle body face, fit some spare ½” AF bolts into the

flange holes. The bolts act as “legs”, supporting the carburettor

off the workbench. Whilst the carburettor is together enough to

get a good grip on it, loosen the fuel inlet fitting (1” AF) and fuel

valve seat lock screw and nut (slot-head/ 5/8” AF).

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12. Undo and remove the four slot-head fuel bowl screws. Separate

the fuel bowl from the metering body – if the gasket is glueing

the two together, a gentle tap with a screwdriver or hammer

handle may loosen it. Retain the old fuel bowl gasket to

compare to the new one from the kit.

13. Undo and remove the fuel inlet fitting (1” AF) and associated

gasket. Pull out the sintered bronze fuel filter, fuel filter gasket

and fuel filter spring (note that these are missing from the

picture to the right). Unscrew the fuel valve seat lock screw

(slot-head), remove the fuel valve seat adjustment nut and

unscrew the fuel valve assembly (5/16” AF). Remove the slot

head fuel level check plug and associated gasket. Pick out the

bowl screw gaskets (which have generally stuck to the fuel

bowl), taking care not to damage the fuel bowl faces.

14. Undo and remove the two slot-head float shaft retainer screws. Remove the float shaft retainer, float

lever shaft, float spring and float assembly as one unit. Take careful note of the relationship between

the float shaft retainer, float lever shaft, float spring and float assembly before disassembling (see

picture below right).

15. Undo and remove the four phillips-head accelerator pump cover screws. Remove the accelerator

pump cover, accelerator pump diaphragm and diaphragm return spring. The hanging ball non-return

valve and retainer (see picture below right) are not removed.

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Note that

late-

production

350 Holley

carburettors

used a

“plastic

umbrella”

non-return

valve. If one is fitted, remove and discard the plastic umbrella.

16. Separate the metering body from the main body – if the gasket

is glueing the two together, a gentle tap with a screwdriver or

hammer handle may loosen it. Retain the old metering body

gasket to compare to the new one from the kit.

17. Unscrew the two main metering jets with a wide-blade slot-head

screwdriver. Carefully remove the fuel bowl gasket, taking care

not to damage the metering block face. Unscrew the two slot-

head idle needle valves and pick out the associated cork seals.

Remove the power valve with a 1” AF socket. Carefully remove

the metering body gasket, taking care not to damage the

metering body face

18. Unscrew and remove the phillips-head

pump discharge nozzle screw. Remove the

pump discharge nozzle and associated

gasket. Turn the main body upside down

and catch the pump discharge needle valve

as it falls out.

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19. Unscrew and remove the five phillips-head throttle body to main body screws. Separate the main

body, throttle body and associated gasket. Remove the slot-head choke air bleed orifice from the

base of the throttle body.

20. Unscrew the slot-head pump cam lockscrew and remove the

lockscrew and pump cam. Undo and remove the accelerator

pump adjustment screw, nut (3/8” AF) and spring. Remove the

pump operating lever retainer and slide off the pump operating

lever. Unscrew the throttle stop screw and spring.

8.4 Cleaning and Inspection

1. Clean all parts in some petrol to remove most of the oil and dirt. Ensure good ventilation and no open

flames when washing parts with petrol (or any of the solvents below). An alternative is to use one of

the spray type “carburettor and throttle body cleaners” available from SuperCheap, Repco etc. Most

of the cleaners available are made for spraying down a carburettor throat with the engine running,

rather than detailed cleaning of a disassembled carburettor. They tend to be mainly solvent,

evaporate very quickly, and are this not much use for “soaking” parts. They are also not very suitable

for removing the carbon (“coke”) that builds up inside carburettors (what little they dissolve tends to

restick as the cleaner evaporates). From trying some of them, I personally believe these spray

cleaners are little (if any) better than using straight petrol for cleaning disassembled carburettors.

Many forums recommend the use of “dip” cleaners to soak parts in (for example Berrymans B9

Chem Dip, which has a number of solvents, cresols and sodium bichromate). Some hunting has

shown that “dip” cleaners are very hard to come by in Australia. One that is available is Yamalube

Carburettor Cleaner, though I have not tried it. Paint thinners also does a fair job of removing the

gunk. Note that the plastic choke link seal will be left in the airhorn – whilst it is tolerant of a short

bath in petrol or thinners, soaking it for an extended period is not advisable. The same goes for the

plastic pump cam.

2. Blow out all passages with compressed air in the opposite direction to normal flow. Do not rod-out

any jets or passages with drills or wires unless absolutely necessary as it is likely to change their

flow characteristics. If a compressor is not available, a bicycle pump (with a ball inflation needle

fitted) will do the task.

3. Use a steel rule to check that the main body assembly, metering body and float bowl are flat where

they join. Should any of these surfaces not be flat, replacement may be required. Whilst the main

body can be machined flat (within reason), the metering body and float bowls each have gasket

sealing beads. Machining these parts removes the beads, causing difficulty in gasket sealing.

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4. Check the idle discharge holes and transfer slots in the throttle body assembly to make sure they

have no carbon deposits.

5. Examine the idle needle valves. If they are ringed or grooved they must be replaced.

6. Inspect the main metering jets to ensure they are clean and unmarked.

7. Check the float assembly for dents and punctures (for example the float

on the left of the image is severely dented, either from being used in a

blow-through forced induction system, a severe backfire, poor handling

during reassembly or being used in a dual-fuel (LPG) vehicle).

8. Check the throttle lever and shaft assembly where it passes through either side of the throttle body

assembly (62) for looseness. Worn assemblies should be professionally rebushed during the rebuild.

Check that the throttle valve opens and closes correctly. Check that the throttle plate screws are tight

and staked.

9. Check the choke shaft assembly where it passes through either side of the air horn for looseness.

Check that the choke valve assembly opens and closes correctly and

that the choke plate screws are tight and staked..

10. With the fuel bowl inverted, check the clearance between the accelerator

pump check ball and the retainer bar. The clearance should be 0.011-

0.015”. Note that in order to do this a set of feeler gauges will need to be

modified (narrowed and bent…a handy hint is to bend them first then file

them narrow, as they don’t like being bent once they are narrowed). The

retainer bar can be bent gently, though care needs to be taken not to pry

the bar from its end fittings.

8.5 Assembly

When assembling the carburettor, the bolts and fittings may be torqued. Whilst not absolutely essential, torqueing to a set value can prevent stripping threads (most of the screws are into alloy), or uneven tightening (leading to leaks). The following torque settings should be applied during assembly. Note that the values are in inch-pounds (not foot-pounds!).

Application Fastener Size-Threads Per

Inch

Torque Range Minimum-Maximum

(inch-pounds)

Dry Oiled

Fuel bowl screws 12-24 25-30 19-22

Main metering jets ¼-32 30-40 20-30

Fuel valve seat lock screw ¼-32 50-60 40-45

Float shaft retainer screws 6-32 3-5 2-3

Fuel bowl inlet fitting 7/8-20 200-250 150-190

Power valve ½-28 40-50 30-38

Accelerator pump cover screws 8-32 6-10 5-8

Choke vacuum restrictor grub screw 10-32 10-15 8-11

Fuel level check plug 5/16-24 55-65 40-50

Choke housing screws 8-32 6-10 5-8

Pump discharge nozzle screw 12-28 25-30 19-22

13. Install the pump cam and slot-head pump cam lockscrew into position #2 of the throttle shaft.

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14. Install the accelerator pump adjustment screw, nut (3/8” AF) and spring to the pump operating lever,

leaving them loose for now.

15. Install the throttle stop screw and spring into the throttle body.

16. Fit and tighten the slot-head choke vacuum restrictor grub screw into the base of the throttle body.

17. Using the new throttle body gasket from the kit, fit together the main body and throttle body. Take

care that the correct gasket is chosen from the kit. Tighten the five phillips-head throttle body to main

body screws.

18. Fit some spare ½” AF bolts into the throttle body flange holes. The bolts act as “legs”, supporting the

carburettor off the workbench.

19. Install the pump discharge needle valve. Using the new gasket from the kit, install the pump

discharge nozzle and tighten the phillips-head pump discharge nozzle screw. Set aside the

throttle/main body assembly for now.

20. Screw the two main metering jets into the metering block with a wide-blade slot-head screwdriver.

21. Using new cork seals from the kit, install the two slot-head idle needle valves into the metering block.

Screw them in gently until they seat (do not overtighten!) then back them out 1½ turns.

22. Install the power valve and gasket (both from the kit) into the metering body with a 1” AF socket. Set

aside the metering block assembly for now.

23. If the pump non-return valve is the “plastic umbrella” type, install a new “umbrella”. Wet the umbrella

nipple with some spit, then insert the umbrella nipple from the outside of the fuel bowl and gently

pulling it through from the inside. You will feel the nipple “click” as it seats. Cut the top off the nipple,

leaving a small amount protruding into the fuel bowl (if the whole nipple is left it will interfere with the

float at low float level).

24. Place the new diaphragm return spring into the accelerator pump housing. Fit the accelerator pump

diaphragm from the kit over the spring, taking care to select the 30cc diaphragm from the kit. Fit the

accelerator pump cover then install and tighten the four phillips-head accelerator pump cover

screws.

25. Reassemble the float shaft retainer, float lever shaft, float spring and float assembly as one unit.

Install the assembly into the fuel bowl, tightening the two slot-head float shaft retainer screws.

26. Install the new fuel valve assembly from the kit, using the adjustment screw and locknut gaskets

from the kit. Install the fuel valve seat adjustment nut and the slot-head fuel valve seat lock screw.

27. Note that there are three types of float construction: hollow brass (left image below), solid black

nitrophyl (centre image below) and hollow white Duracon (right image below).

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For brass and nitrophyl floats, turn the fuel bowl upside down, then

adjust the fuel valve seat adjustment nut until the float sits in the middle

of the fuel bowl (as per the image to the right). Tighten the slot-head

fuel valve seat lock screw.

Duracon floats ride higher on the fuel than either the brass or nitrophyl

float and, therefore, a higher setting is in order. For Durcon floats, turn

the fuel bowl upside down, then adjust the fuel valve seat adjustment nut until the float sits 5/16”

from the bottom of the float bowl (the side with the adjustment nut), measured at the middle of the

float (a drill bit is handy to measure with). Tighten the slot-head fuel valve seat lock screw.

28. Install and tighten the slot head fuel level check plug, using the new check plug gasket from the kit.

29. Assemble the main body assembly, metering block and fuel bowl, using the new fuel bowl gasket

and metering block gasket from the kit. Whilst the fuel bowl gasket is normally symmetrical, the

metering block gasket is not, and care must be taken that it is not put in back-to-front – check the

alignment of the holes in the gasket with those in the metering block.

30. Install and tighten the four slot-head fuel bowl screws, using the new plastic bowl screw gaskets from

the kit.

31. Fit the pump operating lever, screw, spring, locknut and retainer.

32. Ideally, the accelerator pump operating lever should just be in contact with the short pump arm

(mounted on the accelerator pump cover) at idle. This absence of slack

gives sharp accelerator pump response. However, the accelerator pump

operating lever needs to be set such that it does not overflex the pump

diaphragm. To set the operating lever clearance, tighten the locknut such

that the pump operating lever is just in contact with the short pump arm.

Next, hold the throttle fully open, then move the pump arm until the pump

diaphragm is fully flexed. Measure the gap between the pump arm and the pump operating lever

adjustment screw with a set of feeler gauges. If the gap is less than 0.015”, back off the locknut to

suit. This will mean that there will be a slight throttle response delay (due to the operating lever

having to move a little bit before it contacts and starts to move the pump arm), but this is preferable

to overflexing (and tearing) the pump diaphragm.

33. Reassemble the three separate choke assemblies (fast idle pick-up lever, fast idle cam lever spring

and fast idle cam lever as one unit, back-up plate and stud assembly, choke rod lever and bushing

assembly and choke spring as a second unit and choke lever and swivel assembly, fast idle cam

plate and fast idle cam and shaft assembly as a third unit.

34. Install the fast idle pick-up lever, fast idle cam lever spring and fast idle cam lever as one unit and

hold it in place with the phillips-head fast idle cam lever screw.

35. Fit a new paper circle gasket from the kit to cover the choke vacuum passage. Holding the gasket in

place, fit the back-up plate and stud assembly, choke rod lever and bushing assembly and choke

spring as one unit. Install the choke link hairpin clip to the choke link.

36. Install the choke lever and swivel assembly, fast idle cam plate and fast idle cam and shaft assembly

as one unit. Install the single slot-head screw to hold it in place, then fit the choke cable holder

bracket with it’s two slot-head screws.

37. Adjust the fast idle screw with the choke fully open such that the gap between the throttle plates and

the throttle bores is 0.020”. This is pretty small to measure with a set of standard drill bits, so again a

“bent and narrowed” feeler gauge is handy.

38. Set the throttle stop screw such that the throttle plates are closed, then back the screw out 1½ turns.

39. Install the fuel filter spring, new sintered bronze filter and fuel filter gasket from the kit. Install and

tighten the fuel inlet fitting (1” AF), using the new gasket from the kit.

40. Before putting the carburetor onto the vehicle, it is wise to double check (triple check) that the parts

that can fall through into the carburettor throat are staked and/or tight:

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pump nozzle screw tight. Although the screw and nozzle cannot pass into the engine (won’t fit

past the booster venturi), the pump check valve “needle” certainly can.

hot air choke restrictor grub screw tight.

Choke plate screws tight and staked.

Throttle plate screws tight and staked.

41. Install the carburettor to the manifold using the new gasket from the kit. Do not tighten the flange

nuts just yet as the ability to move the carburettor slightly makes some of the connections easier.

Note that the throttle bores are not centered on 350 Holley carburettors, and are offset 0.17” (~11

/64”)

to the back of the flange. If the carburettor flange gasket is put in back-to-front, it may catch the

throttle plates, causing them to jam open

42. Connect the choke control cable to the choke actuation lever, and mount the outer sleeve to the

cable clamp. Actuate the choke cable through its full range of motion to ensure full choke operation

and adjust as necessary.

43. Connect the fuel line to the carburettor fitting.

44. Connect the manifold vacuum hose at the rear of the throttle body base, and the timed spark vacuum

hose at the side of the metering block. Note that in some cases either or both of these hose

connections may be not used, and must hence be capped off at the carburettor with plastic caps.

45. Install the throttle cable to the clamp and to the carburettor. Refit any throttle return spring(s)

required.

46. On automatic transmission vehicles only, install the transmission kickdown adjustment screw and

black retaining clip, as correctly indicated. Failure to attend to this detail may

result in a sticking wide-open throttle or dangerous uncontrolled engine

speed.

47. Tighten the manifold flange bolts to 15ftlb in the pattern shown in the image

to the right. Do not overtighten the nuts, as a warped or cracked throttle body

may result.

48. Check that the throttle operates smoothly and returns to idle. Check that wide

open throttle (WOT) is achieved.

49. Start the engine and check the fuel lines and inlet fitting for possible leaks.

50. Place the air cleaner gasket (not supplied in the kit) on the sealing flange, and install the air cleaner.

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9 Tuning

9.1 Fuel Level

Fuel level is adjusted so that the vehicle does not run out of fuel (lean out)

under cornering or acceleration (too low) or burp uncontrolled into the

engine (too high).

To set the fuel level:

1. Start the vehicle. 2. Remove the fuel bowl sight plug. 3. Observe the sight plug hole for the fuel level. If none is seen, the

level is too low - fuel should be even with the bottom of the sight plug hole. If fuel comes pouring out of the sight hole, the float is set too high.

4. To adjust the float level, shut down the engine. 5. Loosen the lock screw on top of the fuel bowl just enough to allow you to turn the adjusting nut. Hold

the screw in position with the screwdriver. 6. Turn the

5/8” AF adjusting nut in the appropriate direction: clockwise to lower float and

counterclockwise to raise float. Turn the nut in increments of ¼ of a rotation. 7. Retighten the lock screw. 8. Restart the vehicle and observe the sight plug hole. Repeat steps 4. – 7. as necessary. Note that there are a variety of Viton-tipped needle and seat combinations available for 350 Holley carburettors, ranging from 0.097” seat diameter to 0.110” diameter. Steel and titanium needle and seat assemblies (not recommended for street use but required for methanol use) are available up to 0.150” seat diameter. Installing too small a needle and seat means that the engine can starve under high load. Installing too large a needle and seat means that control over the fuel level will be more sloppy. The chart below shows the fuel flow through various needle and seat sizes at different fuel pressures. Note that for early Holdens (running at 3-6 psi of fuel pressure) there is no benefit in changing to a larger needle and seat size (even the 0.097” diameter seat will flow twice the early Holden fuel demand).

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0

10

20

30

40

50

0 1 2 3 4 5 6

Fue

l Flo

w (

GP

H)

Inlet Pressure (psi)

0.082"

0.097"

0.101"

0.110" (holes)

0.110" (windows)

0.120"

early Holden fuel demand

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9.2 Idle Speed and Idle Mixture

Engine idle speed (often referred to as “curb idle”, the speed the engine runs at when warm with the

choke off) is adjusted so that the vehicle does not stall when stationary (too low) or consume excess

fuel/jump when moving off (too high). Idle mixture is set to provide a good fuel/air combination (neither too

rich nor too lean) when stationary. Whilst idle speed and idle mixture can be set “by ear”, there are some

tools that make it easier/more consistent:

A tachometer (either dash mounted or fed from the ignition leads) can help accurately set idle speed.

If a tachometer is unavailable, a timing light can be connected and the number of “flashes” in twelve

seconds counted. Multiply the number of flashes by ten to get the RPM. This is pretty hard to do

though – you are looking to count around four flashes per second.

A vacuum gauge (either dash mounted or a removable pressure gauge that screws into the inlet

manifold after disconnecting the vacuum wipers (FB and earlier Holdens) or power brake/windscreen

washers (NASCO accessories) from the manifold. The vacuum gauge gives a more accurate setting

to the idle mixture than the “back it off until it runs smooth” method.

To set the idle speed and mixture:

1. Warm the car up to normal operating condition. Check the choke is off. Leave the air cleaner in

place.

2. Fit the vacuum gauge to a vacuum manifold port on the carburetor and the tachometer (where

available).

3. Adjust the curb idle speed screw until the engine idles at 480-520 rpm (check with a tachometer,

timing light counting or “by ear”).

4. Adjust the two idle mixture screws 1/8 of a turn at a time, alternating between each screw. Turn them

equally, until you achieve the highest possible vacuum reading without adjusting the curb idle speed

screw. If a vacuum gauge is not available, use a tachometer (or your ear) to obtain the highest

possible RPM.

5. Check the engine speed again, and repeat steps 3. and 4. above until a satisfactory idle is achieved.

6. Remove the tachometer and vacuum gauge and refit any vacuum lines that were disconnected.

If a rough idle persists after the mixture screws have been adjusted, check for vacuum leaks. These could

result from unplugged vacuum fittings, carburetor flange gaskets that were torn during installation,

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cracked lines or loose bolt/screws. A quick way to check vacuum leaks is to spray WD40 in the suspected

area with the engine running – if the engine speed increases, there is a vacuum leak.

Note that on vehicles with very lumpy cams, the large amount of valve overlap can mean that there is

very little vacuum at idle (6”Hg or less). At times, these vehicles may not respond well to setting the idle

mixture – the idle mixture screw seems to do little to help the idle. The low engine vacuum at idle means

that the throttle plates need to be opened more than usual to draw fuel from the idle system… in fact they

can be opened so much that the idle transfer slots are uncovered, leading to excessively rich idle (and no

control of the idle mixture as the idle needle valve only controls the lower idle discharge hole). To check

for this, set the idle as best as possible, then remove the carburettor and check the throttle plate position

– if more than 0.030” of the idle transfer slot is exposed, then this may be the cause of the loss of idle

control. One method to fix this is to drill a 1/16” hole in the throttle plate on the same side of the shaft as

the idle discharge holes. The small hole will allow some air to pass, allowing the throttle plates to be

closed further and idle mixture control regained. The hole can be enlarged by stepping up drillbits in 1/32”

increments until the throttle plates are sufficiently closed (don’t go too large or the throttle paltes will be

fully closed, giving an off-idle flat spot). This condition should not be confused with an early opening

power valve – see Section 8.8 below.

For some vehicles, even with the idle mixture screws turned all the way in (lean), it may not be possible to

obtain a satisfactorily lean idle mixture. In these cases the idle feed restriction may be closed up, or the

idle air bleed enlarged. Modifying the idle feed restriction is preferred, as it does not affect the timing of

the idle system. However, the 350 Holley idle feed restriction appears to be inside the idle tube, making

this a difficult task. Whilst it is simple to “drill out” the idle air bleed, this will cause the idle system to start

flowing later. Modifying the idle feed restriction and idle air bleed should not be taken lightly, and should

be avoided where possible.

Whilst early Holdens, being manufactured prior to July 1972, are generally not required to comply with

emission standards. However, from that date onwards, all petrol passenger vehicles (and derivatives)

were required, when new, to comply with a performance standard (ADR) that set limits for exhaust

emissions of hydrocarbons (HC), oxides of nitrogen (NOx) and carbon monoxide (CO):

ADR26 was introduced 1/1/1976, and captures the CO at idle test (limit of 4.5% maximum volume

CO).

ADR27, 27A, 27B and 27C applied to vehicles manufactured from July 1976 to January 1986.

Vehicles made in this period generally ran on leaded petrol and employed carburettors.

ADR37/00 covers the period from February 1986 to the present. Vehicles manufactured after

January 1986 generally run on unleaded petrol (catalytic convertors), with computerized engine

management systems, fuel injection.

A summary of the emissions requirements of each of the tests above can be found here:

http://www.infrastructure.gov.au/roads/environment/impact/emission.aspx. Most early Holdens will not

have to conform to the above. However, some engineers request the CO at idle test when vehicles have

been modified to the extent that they require an engineer’s report. It is important to note that the idle test

is normally done at idle (480-520rpm). There is an alternative “high idle” test, which is conducted at

2500rpm. This test, although usually not applied to early Holdens, will bring the main metering circuit into

play (i.e. tuning for the CO at idle test is made via the idle needle valve (59), tuning for the “high idle test”,

if it was ever applied, is by changing the main metering jet). To tune the idle circuit to meet a CO at idle

test, an engine exhaust analyser is used – these are discussed more fully in Section 2.5.4 below. When

tuning for emissions, a CO at idle reading of 1-3% should be targeted.

http://www.infrastructure.gov.au/roads/environment/impact/emission.aspx

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9.3 Fast Idle Speed

Fast idle is the speed that the engine runs at when the choke is on. To set the fast idle speed, 1. Start the engine, allowing it to reach operating temperature. Manually

advance the throttle to just off idle. Push the fast idle cam up, so the fast idle screw is on the top step of the cam. This fast idle speed should be set to 1500-1600 RPM.

2. To adjust the fast idle speed, shut down the engine and hold the throttle in the wide-open position to expose the fast idle screw below the choke housing. Use a small ¼” open-end spanner for adjustment, turning the screw clockwise to increase the RPM or counterclockwise to decrease the RPM.

3. Start the engine, and recheck idle speed.

9.4 Accelerator Pump

There are three different tuning parameters that may be modified to tailor the accelerator pump action

(how the vehicle initially responds when you put your foot down):

a) Pump discharge nozzle size,

b) Pump cam profile (colour and position), and

c) Pump capacity.

The amount of fuel that can be delivered by one accelerator pump stroke is determined by the pump’s

capacity and the profile of the pump cam. The period of time that it will take for this pre-determined

amount of fuel to be delivered is affected by the pump nozzle size.

9.4.1 Pump Discharge Nozzle Size Holley accelerator pump discharge nozzles are stamped with a number which indicates the drilled pump

hole size. For example, a pump discharge nozzle stamped “35” is drilled 0.035". Pump nozzle sizes are

available from 0.025" to 0.052". Note that:

whenever a #40 (0.040)" or larger pump discharge nozzle is installed, the “hollow” pump nozzle screw

should also be used. This screw will allow more fuel to flow to the pump nozzle, assuring that the

pump nozzle itself will be the limiting restriction.

whenever a #37 (0.037") or larger pump discharge nozzle is installed, the 50cc accelerator pump

should also be used.

The following guidelines can be used to tune the pump discharge nozzle:

a vehicle that accelerates well at first then bogs down may be squirting all the fuel shot too quickly.

The fuel shot can have it’s dutation extended by changing to a smaller pump discharge nozzle.

a vehicle which initially hesitates then accelerates smoothly (or gives a lean backfire) may need more

fuel initially. This can be achieved by fitting a larger pump discharge nozzle.

when changing the pump discharge nozzles, jump three sizes at a time. For example if there is

currently an off-line hesitation with a #28 (0.028") pump discharge nozzle, try a #31 (0.031") pump

discharge nozzle.

Once a pump discharge nozzle size selection has been made the accelerator pump system can be

further tailored with the pump cam.

9.4.2 Pump Cam Profile and Position

Holley offers an assortment of different pump cams, each with uniquely different lift and duration profiles.

The cams are colour coded (see graph below), with the standard 350 Holley cam being Orange. The

cams are available as Holley part number 20-12. Switching cams will directly affect the movement of the

accelerator pump lever and subsequently, the amount of fuel available at the pump nozzle. The table

below gives the speed with which each cam delivers fuel, which has been drawn from the first chart

below. The second chart gives the fuel volume delivered by each cam.

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← F

aste

r

sh

ot

Pink

Black

Green, White, Red and Orange

Brown

Blue

Yellow

Whilst the table and charts gives some guidance, the best method of selecting the correct pump cam is

by trial and error – monitoring either “seat of the pants feel”, quarter mile times or circuit elapsed times.

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Cam

in p

osi

tio

n 1

Cam

in p

osi

tio

n 1

Cam

in p

osi

tio

n 2

Cam

in p

osi

tio

n 1

Cam

in p

osi

tio

n 1

Cam

in p

osi

tio

n 1

Cam

in p

osi

tio

n 2

Cam

in p

osi

tio

n 2

Cam

in p

osi

tio

n 2

Cam

in p

osi

tio

n 1

Cam

in p

osi

tio

n 2

Cam

in p

osi

tio

n 1

Cam

in p

osi

tio

n 2

Cam

in p

osi

tio

n 1

Cam

in p

osi

tio

n 2

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Pu

mp

Vo

lum

e (

cc)

Pump Cam and Position

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Note that there are two holes in each pump cam, numbered 1 and 2. Placing the screw in position #1

activates the accelerator pump a little early, allowing full use of the pump’s capacity. Generally, vehicles

which normally run at lower idle speeds (600-700rpm) find this position more useful because they can

have a good pump shot available coming right off this relatively low idle. Position #2 delays the pump

action, which is good for engines that idle at 1000rpm and above. Repositioning the cam in this way

makes allowance for the extra throttle rotation required to maintain the relatively higher idle setting. In

some drag racing applications, the vehicle is staged at considerably higher rpm. Where the full

accelerator pump shot is required at the (high) staging rpm, the pump cam can be rotated such that the

cam is at the start of lift at the staging throttle position. The cam holes are then redrilled for this new

position.

Note that pump arm adjustment and clearance should be checked and verified each and every time the

pump cam and/or pump cam position is changed.

9.4.3 Pump Cam Profile and Position

The standard 350 Holley accelerator pump is a 30cc unit. The larger 50cc unit should be used:

where a #37 (0.037") or larger pump discharge nozzle is installed,

where the brown or yellow pump cams are used (using the 30cc pump with these pump cams can

cause the throttle to jam open).

The 50cc accelerator pump is available as a bolt-on conversion kit (Holley part number 20-11). The main

differences between the 30cc and 50cc pumps are as follows:

Item 50cc 30cc Image (30cc on right)

Accelerator pump cover

Stamped 34R2773

Stamped 34R2178

B

Pump diaphragm

135-14 – deeper

135-12 - shallower

Diaphragm return spring

4 coils 3 coils

Note that the pump diaphragm cover screws are

7/32” longer for the 50cc pump.

The accelerator pump cover is thicker in the 50cc unit. This may necessitate the use of a ¼” (or thicker)

spacer between the carburettor and manifold in order for the pump cover arm to clear the manifold.

Another method used is to carefully grind a crescent in the inlet manifold to give the pump cover arm a

slot to operate in.

9.5 Main Metering Jets

Holley main metering jets are broached, flowed, and stamped according to flow rate. The stamped numbers are reference numbers and do not indicate drill size (for example, #88, #89 and #90 jets all have a 0.104” diameter hole). As Holley jets are widely available, there is no need to redrill a Holley jet (in any case,

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modification of the chamfers – see the image above left - on the jet by drilling can make the resultant jet flow very different rates to what would be expected). Holley main metering jets are available in sizes from #40 – #156. A higher relative number indicates a larger jet size. Standard main jets have a 3% tolerance in flowrates for a given jet size and approximately 4½% flow difference between jet sizes. A range of close-limit jets are also available with 1½% flow difference between jet sizes. Changing to a larger or smaller jet will either richen or make leaner the carburetor’s fuel curve from part throttle to full throttle, respectively. When changing the carburetor jetting, it is recommended to jump two jet sizes (e.g. change from a #60 to a #62 main metering jet). As there is only 4½% flow difference from one jet size to the next, changing one size won’t make that much of a difference.

Listed below is a recommended jetting range for various Holden engine sizes using the 350 Holley carburetor. This jetting size is a good general guide only and will vary from engine to engine depending on the degree of modification.

Engine Capacity

(Ci)

Main jets

Without venturi sleeves With venturi sleeves

149 #55 #49

161 #57 #50

179 #58 #51

186 #60 #53

192 #60 #53

202 #61 #54

If a vehicle is changing operation to a higher altitude, air is thinner so decrease the jet size one number for every 2000’ (600m) increase in altitude.

There are a number of ways to select the correct main metering jet (or correctly adjust an adjustable main metering jet):

reading the spark-plugs,

measuring exhaust gas carbon monoxide, and

running the car on a dyno/strip (more applicable to the power bypass jet – see below).

Each of these methods should be undertaken in conjunction with road testing, looking for stumbles, flat spots, drivability and fuel consumption.

Reading the colour of the spark plug electrodes (and to a lesser extent the colour of the exhaust pipe) provides a cheap and easy guide to correct main metering jet choice. This technique involves driving the vehicle for a run (up to operating temperature and a moderate distance at “cruise” conditions – not all at idle or full throttle!). After stopping then cooling down the engine, each plug is removed in turn and the colour of its electrode compared. Today the use of unleaded fuels and high-energy ignition systems has made this method much harder because very little color is seen on the spark plug; however the pictures below give some guidance:

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A more full description of spark plug readings can be found at http://www.classiccarhub.co.uk/articles/spark_plugs.html. A much more accurate way to tune the main metering jets is to measure the carbon monoxide (CO) in the

vehicle exhaust. CO is one of the gases in the engine exhaust (along with nitrogen (N2), carbon dioxide

(CO2), water (H2O), hydrocarbons (unburnt fuel, often written as HC), and various nitrogen oxides (NOX)

and sulphur oxides (SOX). The amount of CO in a vehicle exhaust is an indicator of the air/fuel mixture

being supplied to the engine, and thus is an excellent way of tuning jet sizes on carburettors.

Manufacturers typically specify a CO level somewhere within the range 0.5% to 3.5% by volume. At CO

levels higher than this there is a loss in economy, and at very rich settings, typically 8% to 10% CO, the

onset of poor running occurs, characterized by the particular engine sound that is known as “hunting”. It

should be noted that an engine, even in good overall condition, will show a fluctuation in idle CO over a

period of time, of typically 0.5%. To measure CO, a sample probe is placed into the exhaust pipe and an

exhaust gas analyser unit “reads” the CO in the exhaust. The other readings that some exhaust analyzers

provide include HC (the best mixture gives you the lowest HC), CO2 (the best mixture gives you the

highest CO2 reading) and O2. Whilst workshop units can cost in excess of $4000, a simple and cost

effective exhaust analyser (the “Gastester Digital”) is available from Gunsen for around $250 (see

http://www.gunson.co.uk/item.aspx?item=1835). This would not be a bad investment if you are

planning to tune a few early Holdens over the years. Using this analyser, some starting points for tuning

would be to tune to 0.75-1.25% CO (1–3% CO for a lumpy-cammed engine) at cruise conditions.

9.6 Power Valves

There are two different parameters that may be set for the power enrichment system – the time (or vacuum) at which it comes on, and the amount of fuel which is flowed. The number stamped on a power valve, such as 65, indicates the manifold vacuum below which the power valve is operational. In this case, all manifold vacuums below 6.5” Hg, the power valve is operating. The factory “out of the box” power valve for 350 Holley carburettors is a standard-flow 85 (Holley part number 125-85). For most early Holden applications, a 65 power valve is suitable, provided

Overly lean (main metering jet is too small). Whitish or pale deposits. May also be seen by erosion of the spark plug electrode or detonation damage of the insulator.

Correct jetting: electrode deposits are slight and not heavy enough to cause any detrimental effect. Colour is brown to greyish tan colour, and minimal amount of electrode erosion.

Overly rich (main metering

jet is too large): Soft, black,

sooty deposit.

http://www.classiccarhub.co.uk/articles/spark_plugs.html

http://www.gunson.co.uk/item.aspx?item=1835

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the manifold vacuum is 12”Hg or higher. However, vehicles with a large overlap cam can idle at 6.0”Hg. At this vacuum, the power valve has opened and is starting to feed the mixture, leading to the vehicle “loading up” at idle. To correct this problem, install a lower-numbered power valve (e.g. a 55, 45 or 35 power valve). If the engine has a manifold vacuum of 12”Hg or less, a simple way to determine power valve size is take the manifold vacuum at idle and divide that number by two. The answer is the power valve size. For example a vehicle with an idle manifold vacuum of 9”Hg, a power valve of (9 / 2 =) 4.5 is reasonable. Holley power valves come in two different types – a standard flow and a high-flow. The high-flow power valves will flow more fuel, though it should be noted that the power valve does not usually control the fuel flow – the Power Valve Channel Restrictions (PVCRs) do.

The following table gives the Holley power valves available:

Part No. Flow Vacuum opening (“Hg)

125-1005 High 10.5

125-105 Standard

125-95 Standard 9.5

125-185 High 8.5

125-85 Standard

125-75 Standard 7.5

125-165 High 6.5

125-65 Standard

125-155 High 5.5

125-55 Standard

125-50 Standard 5.0

125-145 High 4.5

125-45 Standard

125-135 High 3.5

125-35 Standard

125-125 High 2.5

125-25 Standard

125-10 Standard 1.0

As indicated above, the amount of fuel which is flowed is determined by the PVCR. These are located in

the metering block, and are able to be drilled to larger sizes to richen the fuel mixture under load. PVCRs

which have been over-enthusiastically drilled and are too large can be reduced in size by inserting small

vee-shaped lengths of wire into the PVCR.

One method to tune the power valve (PVCR diameter and best vacuum opening point) is to use timed acceleration runs (e.g. ¼-mile times), or top speed/power (e.g. dyno-tuning). This involves trial and error jetting changes to obtain the best results, and needs some moderate track or dynamometer time to get decent repeatable results. An easier way is to again tune using an exhaust analyser (particularly if you have the Gunson exhaust analyser described in above). Some starting points for tuning would be to tune to 6.6% CO under load conditions. Whilst this could be reduced to 4% for engines with very good combustion chamber design, early Holden cylinder heads rarely meet this criteria. For vehicles that run wide-open throttle most of the time (like HQ Holden circuit racers), the power valve is often removed (blanked off with blanking plug part number 26-36) and the main jet sizes increased 6-8 jet sizes to suit. Whilst this is suitable for full throttle performance, it will lead to a very rich “cruise” condition and is not recommended for street use.

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If a vehicle is changing operation to a higher altitude, less vacuum is made by the engine so decrease the power valve setting 1.5-2”Hg for every 3000’ (900m) increase in altitude. Note that it is possible to damage the power valve by engine backfire. For carburettor built after 1992, a

power valve blow-out protection system (a ball check valve is located in the throttle body, designed to be

normally open but which quickly seats to close off the internal vacuum passage when a backfire occurs)

is installed. Once closed, the check valve interrupts the pressure wave caused by the backfire, thus

protecting the power valve. A kit is available to retrofit the power valve blow-out protection system to pre-

1992 350 Holleys – see below.

9.7 Venturi Sleeves

Venturi sleeves increase air speed through the venturi, which help prevent flat spots and assists with low-down acceleration. Venturi sleeves should be used on Holden 149 and 161 engines when using a Holley 350 carburetor. Main jet sizes must be reduced when using these sleeves (see table above). It is also recommended to close up the two power valve channel restrictions in the metering block from 0.060” to 0.030”. This can be achieved by inserting bent vee-shaped wires or by fitting brass bleeds, though this can be a difficult process and it may be worthwhile putting up with a slightly rich power system for everyday (not race dedicated) use. Redline Performance venturi sleeves are available from American Auto Parts (part number 14-35) and Barnes Performance (part number BP14-35). The Redline Performance venturi restrictors are 0.035” thick (~

1/32”), and will change a Holley 7448 venturi diameter from 1

3/16” diameter to 1.118” diameter (~1

5/32”).

The venturi restrictors are fitted into the top of the venturi (with the gaps over the booster venturis) and epoxied in place. The gap in the sleeve does not close up – it leaves a gap down the venturi wall. Note that venturi sleeves will slightly reduce the flow capacity (the 350 Holley is reduced from 350CFM to approximately 320CFM). To install venturi sleeves:

1. Whilst it’s possible to install the venturi restrictors with the carburettor still on the vehicle, there is a fair

risk that you will drop something down the carburettor throat. It is strongly recommended that the

carburettor be removed before fitting the venturi restrictors.

2. Clean the venturis and the outside of the venturi sleeves with some thinners to remove any coke,

grease or fuel.

3. Unscrew the retaining screw and remove the accelerator pump discharge nozzle, screw and gaskets.

4. Place a small piece of PVC tape across the top of the accelerator pump discharge hole and another

one across the four air bleeds. This will stop any stray epoxy falling into places it shouldn’t.

5. Drop the first venturi sleeve down past the choke plate. It’s a lot

easier if the choke plate is removed, but not impossible (and

restaking the choke plate screws is a pain in the bum). Resist the

temptation to put the epoxy onto the venturi sleeve before dropping

it in – there is a fair amount of twisting and wiggling to get the

restrictors past the choke plate, which would get epoxy everywhere.

6. Turn the venturi restrictor around so that the slot lines up with the

booster venturi, then push the restrictor into place (dummy fit). It

should be a nice snug fit. The lip on the top of the restrictor stops it

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from pushing down too far down into the venturi (…or into the motor!).

7. Turn the carburettor over and use

a screwdriver to gently poke the

restrictor back out of the venturi,

leaving it sitting on top of the

booster/venturi.

8. Mix some epoxy, and using a cotton bud (or similar spreader) paint the outside of the venturi sleeve

with epoxy. Take care not to get epoxy near the carburettor walls. Use only a thin smear of epoxy and

don’t spread it too close to the edges of the venturi restrictor as it will smoosh out later. Avoid the

temptation to fit and epoxy both restrictors at once… it is a fiddly process, easy to bugger up and the

epoxy goes off quickly.

9. Push the freshly epoxied venturi restrictor into place. Check for any smooshed epoxy (or smears on

the carburettor walls) and wipe it out while it is still wet.

10. Repeat steps 4 – 8 for the second venturi restrictor.

11. Allow the epoxy to set thoroughly. Remove the PVC tape and reinstall the accelerator pump discharge

nozzle.

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10 Troubleshooting

It is common knowledge that “carburettor” is French for “don’t F%@# with

it”. Many Australian children have learnt to swear from listening to the

carefully phrased epithets gently wafting from the open bonnet of an early

Holden. The guidance below may assist in hunting down the cause of

early Holden Stromberg issues (and perhaps prevent your children from

developing their vocabulary). Of note, many ignition and timing issues are

found to be the real cause of what is perceived to be a “bad carby” – the

following table assumes all electrical and timing issues have been

resolved.

Cause

Problem

Sta

lling

Roug

h idle

Flo

od

ing

Hot S

tart

Econo

my

Hesitatio

n

Accele

ratio

n

Surg

e

Back fire (

co

ld)

Pow

er

Sta

lling (

co

ld)

Incorrect idle adjustment

Damaged idle needle

Incorrect fast idle adjustment

Idle passages blocked

Metering jets loose or blocked

Power valve loose or sticking

Fuel inlet needle and seat loose or passing

Float leaking, rubbing or level incorrectly set

Gaskets leaking

Pump discharge holes blocked

Pump diaphragm worn or cut

Pump check ball dirty or sticking

Choke valve and linkage dirty, sticky or damaged

Throttle valve loose, damaged or sticking

Venturi dirty

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11 Modification

11.1 Fuel Supply Stability

11.1.1 Wedged Float

For vehicles which are frequently turning under load (for example

Speedway use and circuit racing), fuel can slosh to one side of the float

bowl. The fuel acting on one end of the float causes it to rises, prematurely

cutting off the fuel supply. To prevent this, a wedged float is available (part

number 116-13). The wedged float is made from nitrophyl, and as the

name suggests has a wedged shape. The wedge is designed so that as

fuel sloshes up the side of the bowl, the fuel will ride up the wedge and

allow the float to stay open and not close off prematurely. The wedged

float is a bolt-in replacement for the original 350 Holley float.

11.1.2 Float Bowl Vent Baffle (Whistle)

For vehicles which are under frequent acceleration (for example drag

racing use), fuel can slosh to the rear of the float bowl and burp out the

float bowl vent. This can lead to overly rich mixtures as the burped fuel is

not metered. To prevent this, a float bowl vent baffle (often called a “vent

whistle”) can be added to the metering block. The vent whistle (part

number 26-89) extends the vent to the front of the float bowl, which is

normally “dry” under hard acceleration. To fit the vent whistle,

1. Remove and dissassemble the metering block.

2. Insert the vent whistle into the metering block

vent hole, protruding towards the float bowl

side.

3. Drill through the top of the metering block

and the top of the vent whistle with a #51 drill

(0.067”).

4. Insert the supplied drive screw through the

metering block and vent whistle. Ensure that

the top surface of the vent whistle is not

depressed (bent down) after installing the

drive screw.

5. Trim the end of the vent whistle so that it fits into the float bowl and has clearance to the front edge

of the bowl.

6. Check that the vent baffle has not sagged as it may contact the float, causing flooding. If it has

sagged, stake the metering body underneath the baffle to raise it.

7. Blow out the metering block with compressed air to remove any drill swarf before reassembly.

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11.2 Higher Air Flow

11.2.1 Choke Horn Removal

One technique for squeezing more airflow (around 30-50 CFM) from a 350 Holley carburettor is to remove the choke air horn and blend the radius of the resulting edge. Whilst the process is simple, it does have it’s downfalls:

Pro Con

More airflow is gained (30-50CFM). The flow increase is small, and may be made more reliably by changing to a 500CFM Holley.

Bonnet clearance is increased. The process is not reversible, unlike the use of a K&N Stubstack (see below).

Material cost is low. The flow increase may be detectable on a dynometer, but is not likely to be noticed “by the

seat of the pants”.

Retains the 350 Holley carburettor (important where carburettor choice is restricted, such as in

Australian Speedway Production Sedan and Modified Production Sedan classes)

The change does not allow the use of the choke, making starting in colder locations difficult in

winter.

To get the full benefit, some epoxy needs to be added to the top of the carburettor air-horn. This

may be susceptible to cracking off (and falling into the running carburettor throat) and hence required

periodic checking.

The process is undertaken as follows: a) Disassemble the carburettor such that the main body assembly is bare. b) Scribe or stamp the List number and date code onto the underside of the air filter mounting plate (the

next guy who tries to work out what the carburettor originally was will thank you for it). c) Hold the main body in a vice (using wooden jaws/packing to avoid marking the faces) and cut off the

choke horn a few millimeters above the top of the main body with a hacksaw. d) Blend the top edges into the venturi with a die-grinder. e) Fill any resultant rough edges (including the now-redundant choke rod hole) with epoxy and sand

smooth. f) Wash out any filings in petrol, then blow through all orifices and channels with compressed air.

Note that in the photographs above I have not shortened bowl vent – this can be brought down to approximately

7/8” tall and mitred similar to the original.

It is important to realize that the increased airflow gained from removing the choke horn can change air/fuel ratios – the carburettor should be retuned after installing one.

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11.2.2 K&N Stubstack

An alternative to removing the choke horn in search of more airflow is to use the K&N Stubstack (K&N part number 85-021 for 350 Holley carburettors). The Stubstack is designed to increase the airflow of carburetors (typically 20-40 CFM, Hot Rod magazine's testing showed an increase of 28 CFM on a 650 Holley and 40 CFM on an 850 Holley, other testing has found 30 CFM on an 850 Holley) by decreasing the restriction around the choke horn. It reduces turbulence, improving metering accuracy. The Stubstack fits inside the air cleaner housing and slides snugly down over the choke horn. It is installed by loctiting into place on the choke horn whilst holding the air filter retaining nut finger tight. When installed on some models, there may be a slight gap at the base, however this is normal and will not affect performance. Due to space limitations between the choke horn and some air cleaner baseplates, the Stubstack has two thin spots in the casting. These will sometimes crack or chip slightly, but does not affect the performance. Whilst the Stubstack has been designed to work effectively with K&N Filtercharger™ elements and 360° custom air cleaner assemblies, many enthusiasts have found that it works equally well with other filters provided the minimum height above the stack is at least 1½" (preferably 2-3”), with best results obtained with large diameter filters of 4-5” height. This is not always possible with low bonnet clearances. It is important to realize that the increased airflow gained from installing a Stubstack can change air/fuel ratios – the carburettor should be retuned after installing one.

11.3 Automatic Choke

350 Holley carburettors came from the factory with manual chokes. The manual chokes fit well with the

FB/EK Holden dash, as the original Holden choke knob and cable can be used to drive the 350 Holley

choke and looks factory. However, for ease of driving it is possible to convert the choke to either electric

or hot air. Whilst conversion to electric choke is the far simplest option, I will cover both electric and hot air

chokes here for the sake of completeness.

11.3.1 Automatic Choke Operation

Electric and hot air chokes operate almost identically – the only difference is the heat source they use.

Just like the manual choke, the choke plate is connected by a link rod that passes down through the air

cleaner mounting boss to the choke assembly. The rod is connected a choke housing lever. The lever is

put under tension by a coil spring which holds the choke in the closed position when the coil spring is

cold. If the coil is warmed up, it expands and slowly moves the choke housing

lever/choke link rod/choke plate to the open position. The amount of tension in the

spring determines how much heat is required to get the spring to start moving. The

tension can be adjusted (by manually winding the spring up or down) by rotating

the choke housing cap a few degrees either way. A series of marks on the cap

show just how far it has been turned. One mark (the “index mark”) is normally

bigger than the others and is used as the reference point. Rotating the cap

anticlockwise to make the choke stay on longer is referred to as “richer”, whilst rotating the cap clockwise

to make the choke open earlier is referred to as “leaner”. Both RICH and LEAN are cast into the choke

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cap as a reminder. The choke coil must be adjusted so that it opens the choke plate at the proper speed

as the engine warms up - slowly enough to prevent lean stumbles; yet fast enough to prevent over-rich

mixtures.

The heat source for a hot air choke is the engine warmth. A small amount of

air is drawn from a clean place, often by tapping into the air cleaner (the

image to the right shows a Model 2300 carburettor where the air cleaner

bosses have been drilled and a tube fitted to allow clean air to be drawn from

the air cleaner). The clean air is then routed past a source of heat – often a

choke stove in the exhaust manifold or inlet manifold crossover. If the engine

is cold, the air is also cold, As the engine warms up, so too does the air flow.

The “hot air” then passes into the choke housing past a small brass piston (we’ll come back to that small

piston later) and past the coil spring. The “hot air” provides the heat to warm up the coil spring. The spent

air then flows through a small vacuum port in the side of the carburettor (see red arrow in diagram to the

right above). This port is present in all 350 Holley carburettors,

though with manual chokes fitted the port is either covered with a

gasket or is lead-filled. The air flows down a channel in the main

body, through a channel in the throttle body and into the inlet

manifold (manifold vacuum is used to “suck” the air along). A

small screw-in brass restrictor (0.055” diameter or #54 drill) in

the throttle body is used to control the rate of the air flow (the

orifice is present in all 350 Holleys, including those with manual

chokes – see red arrow in the diagram to the right). For an

electric choke, the same air flow occurs, but the air source is not

heated (it is often still drawn from the air cleaner, but does not

pass through a hot air stove). Here the air flow is used to prevent the electric choke coil from burning out.

Heat for the electric choke is supplied by electricity warming the coil (just like a toaster element). The

electrical power is turned on when the vehicle ignition is switched on, starting to slowly warm and unwind

the choke spring. Even when the engine is hot, the choke spring normally has power supplied to it.

Without the air flow, the choke coil would soon burn out.

The air flow path can be seen in the image to the

right:

1. hot air enters the choke housing,

2. passes through a channel and into the main

housing compartment,

3. flows over the choke coil (removed in this

photograph) which warms the coil,

4. flows past the choke pull-off piston,

5. passes through a further channel, and

6. exits the choke housing to flow to the throttle

body.

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Having the choke plate fully shut is fine for initial starting as it puts a lot of vacuum on the fuel system (at

the low engine speeds developed by the starter motor there is precious little vacuum, so closing the

choke plate helps conserve what little there is). However, when the engine first fires the vaccum available

is much larger, and the engine requires to be fed some air. A fully closed choke plate will cause the

engine to be overly rich, and can stall or flood. To prevent this, the choke plate is cracked open slightly as

soon as the engine fires. This is done by the small brass piston mentioned above, called the choke pull-

off. The choke pull-off has the air flowing past it for the choke supply. At low engine speeds (when the

starter motor is turning) there is not enough vacuum (and hence not enough air flow to the choke) to

move the small brass piston. Once the engine fires, vacuum increases (as does air flow to the choke).

This causes the choke pull-off piston to move, overriding the choke coil spring and cracking open the

choke plate. After a minute or so of operation, the choke coil spring has

warmed up and opens the choke plate even more, making the choke

pull-off redundant. Note that the choke pull-off piston only just cracks

the choke plate open – if it opens too much, the engine could hesitate,

backfire through the carburettor or stall from having too little choke

function. The amount the choke plate is cracked open by the choke

pull-off is adjustable, often by bending a linkage rod or by an

adjustment screw. The choke pull-off can be seen in the image to the

right.

The choke linkage also incorporates a fast idle cam (the red plastic

item in the image to the right). The fast idle cam bumps open the

throttle a small amount when the choke is opened, increasing engine

speed. The fast idle cam has a number of “steps” that are ridden by the

fast idle screw. As the engine warms and the choke closes, the fast idle

cam rotates, the fast idle screw drops down to lower “steps” and the

throttle closes back to the curb idle speed. When the choke pull-off

cracks the choke plate open, pushing the accelerator pedal allows the

cam to rotate so that the fast idle screw will drop from the highest

(fastest) step and align with the second highest (second fastest) step of

the fast idle cam. Note that adjusting the choke pull-off may also

change the fast idle cam position and vice-versa.

If the vehicle has flooded, the spark plugs will be wet and will prevent the engine firing. If the accelerator

pedal is pushed all the way to the floor (and held there), the throttle will rotate open ready to let lots of

lean fuel/air mixture in to dry the plugs. However, the closed choke plate will prevent this air getting in. To

accommodate this, the fast idle cam lever has a small unloader tang on one side. By pushing the

accelerator pedal all the way to the floor, the rotating throttle shaft rotates the fast idle cam lever, the tang

moves forward and butts up against the end of the “steps”, pushing the fast idle cam partly around. This

drives the choke plate manually open (not all the way, but a little bit more than the choke pull-off would

open it). This allows the airflow in to clear the flooded engine. Releasing the throttle allows the choke

spring (or choke pull-off) to resume controlling the choke plate position.

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11.3.2 Electric Choke Conversion

An electric choke kit is made by Holley (part number 45-

223) to replace the manual choke. The kit supplies the

following parts:

a) short black earth lead,

b) long red (sometimes black) 12V positive lead,

c) thermostat housing gasket

d) thermostat housing clamp

e) thermostat housing assembly

f) choke housing assembly

g) choke link

h) fast idle cam lever

i) fast idle cam lever spring

j) choke housing gasket

k) choke link retainer

l) choke housing screws

m) fast idle cam lever screw

n) thermostat housing clamp screws

To install the electric choke kit: a) Remove the carburetor from the vehicle. b) Remove the three choke housing screws securing the manual choke

housing assembly to the main body. Remove the choke link retainer from the choke link and the manual choke backing plate. Keep the retainer for use at a later time.

c) Remove the fast idle cam lever screw. Remove the fast idle cam lever

and fast idle pickup lever and fast idle cam lever spring. Retain the screw, spring, and small pickup lever.

d) Pull the choke housing gasket off and discard it. If the choke vacuum passage has been lead-sealed, carefully drill through the lead (with a drill in a hand chuck) then pick out the hollow ball. Thoroughly clean the mounting surface of the gasket. Blow compressed air through the passage from the bottom of the throttle plate up to make sure the passage is free of blockages. Air should exit from the choke passage.

e) Use the new fast idle cam lever from the kit and the screw, spring, and small pickup lever retained above, as

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shown in the figures below. Assemble the parts onto the throttle shaft. f) Moisten the cork choke housing gasket provided in the kit. Attach it to the vacuum passage hole on

the choke housing assembly. Insert the choke rod through the hole in the lever on the back of the choke housing. Make sure the fast idle cam is above the choke rod. Use the fastener clip retained above to secure the rod to the lever. Position the choke housing assembly to the carburetor main body. It will help to open the throttle slightly to clear the fast idle lever away from the fast idle cam assembly. Note that on most applications, the original choke link will be used. However, on certain carburetors the new choke link supplied with the kit may have to be used.

g) Using the three equal-length long choke housing screws from the kit, secure the choke housing assembly to the main body. Manually operate the choke plate by moving the bi-metal pick-up lever on the front of the choke housing assembly. The choke plate should move freely. If not, check the choke linkage to make sure there is no binding and that the fast idle screw is in alignment with the cam on the back of the choke housing.

h) Install the new thermostat housing gasket onto the thermostat housing.

i) Install the thermostat housing and thermostat housing clamp. Install the clamp so it bows outward from the housing as per the image to the right. Ensure the bi-metal pick-up lever (in the housing) fits into the loop on the bi-metal spring. Check this by turning the housing in both directions. The choke plate should open when rotated clockwise, and it should close when rotated counter-clockwise.

j) Using the three equal-length short thermostat housing clamp screws from the kit, fasten the clamp and thermostat housing to the choke housing assembly. Tighten it enough to hold the thermostat housing in place, but still allow it to be rotated.

k) Rotate the thermostat housing until the mark on the housing aligns with the index on the choke housing assembly. Tighten the clamp screws so the housing cannot rotate. Do not block the fresh air intake.

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l) Correct polarity must be observed when connecting the electric choke wires. Connecting the (+) lead to earth and the (-) lead to a 12V source will result in a direct short and could cause a fire. Use the shortest wire from the kit to connect the bayonet end to the thermostat housing negative terminal marked (-). Ground the eyelet end to the carburetor. Do this under a screw securing the choke housing assembly to the main body.

m) Remount the carburetor on the vehicle. Connect the long wire from the

kit to the thermostat housing positive terminal marked (+). Run the other end of the wire through the firewall using an existing grommet. Connect is to an ignition activated 12V source so that the choke cap only gets voltage when the engine is running – for FB/EK Holdens, this is the from the fuse panel (located under the dash on the driver’s side) via the 15 amp turn signal/heater/backup fuse (the lower one on the picture to the right) at the back of the panel. A blown choke fuse will disable the heater fan, indicators and reverse lights (each of which were either options or standard on FB and EK Holdens). The choke power lead will require a female spade connector on the end to connect onto the male terminal blade at the rear of the fuse panel (a simple push on fit as the male terminal is already present in all FB/EK Holden fuse panels). It is recommended that insulated terminals are used, as many of the FB/EK wiring terminals are bare, and easy to short. Double check with a voltmeter or test light that the choke only has power when the ignition is on. Note that it is not recommended to use the 12V side of the coil for the power source, as it will result in unacceptable choke operation, and could cause engine misfiring, resulting in possible engine damage. If the vehicle has an aftermarket oil pressure switch (for example driving an electric fuel pump), it would be even better to route the power through that switch – that way the choke only gets power once the engine has fired (and has oil pressure), and does not get power (and start opening) if the vehicle is hard to start and cranking for a long time.

n) Start the engine, allowing it to reach operating temperature. Manually advance the throttle to just off idle. Push the fast idle cam up, so the fast idle screw is on the top step of the cam. This fast idle speed should be set to 1500-1600 RPM. Shut down the engine, and hold the throttle in the wide-open position to expose the fast idle screw below the choke housing. Use a small ¼” open-end spanner for adjustment, turning the screw clockwise to increase the RPM or counterclockwise to decrease the RPM. Start the engine, and recheck idle speed.

o) Choke tuning adjustments are listed below. After making final adjustments, start the engine and make sure the choke plate opens completely.

11.3.3 Hot Air Choke Conversion

Whilst a genuine kit is not available, it is possible to fit the 350 Holley carburettor with a hot-air choke from

another Holley carburettor. This tends not to be a common modification though, as it is easier to source a

12V power source for an electric choke than it is to tap a hot air source. The hot air choke operates

similarly to the electric choke described above, with a coiled spring being connected to the choke rod.

When the engine is cold, the spring holds the choke plate closed. A flow of air is drawn into the choke

housing, past the coil and into the carburettor. The air is drawn from a source that will heat up as the

engine does – often by taking air from the air filter and passing it over the exhaust manifold before

feeding to the choke housing. As the vehicle warms up, the hotter air heats the coiled spring. The spring

expand, moving the choke rod to open the choke plate. It can be a challenge to find a source of hot air in

aftermarket manifolds. One solution is to draw air from a clean source (preferably inside the air filter) via a

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thin ductile copper tube. The copper tube is wrapped a few times around the exhaust manifold (or an

extractor pipe) before being connected to the choke housing. The choke housing thread is a weird one,

though a 12.7x0.91 annealed copper tube (from Bunnings) fits over it with a little persuasion..

11.3.4 Automatic Choke Tuning

The following tuning points are available for Holley automatic chokes:

a) Adjusting how much the choke plate pulls open when the engine first fires.

As a starting point, the factory tuning settings can be used. The integral chokes which are bolted

onto 350 Holley carburettors are normally of two types – either with an adjusting screw, or without

one.

If the adjustment screw is present on the side of the choke housing, the following can be used as a

starting point:

Dig the caulking out of the adjustment screw with a

sharp pick.

Remove the choke cap and push the choke pull-off

piston inwards (onto the adjustment screw

shoulder).

Apply light closing pressure to the choke plate,

then use drill bits to measure the gap between the

top edge of the choke plate and the air horn wall

(put the drill bit in parallel to and adjacent to the air

horn vent, but up against the carburettor wall).

Adjust the screw in or out to give a gap of

approximately ¼”. Turning the adjuster screw

counter-clockwise (out) will open the gap, turning

the adjuster screw clockwise (in) will close the gap.

Note that the adjustment screw should be sealed over

again once tuning is finished to prevent vacuum leaks.

If the adjustment screw is not present on the side of the choke housing, the following can be used as

a starting point:

Bend a paper clip so that it has

an 1/8” end.

Remove the choke cap and

insert the paper clip into the

end of the choke pull-off piston.

Feeling gently, hook the paper

clip into the piston bore slot.

Move the piston in until the

edge of the piston slot engages

the paper clip. The piston is

now “pinned” into the bore by

the paper clip.

Apply light closing pressure to

the choke plate, then use drill bits to measure the gap between the top edge of the choke plate

and the air horn wall (put the drill bit in parallel to and adjacent to the air horn vent, but up against

the carburettor wall).

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Bend the piston lever tang to give a gap of approximately ¼”.

Once this basic setting has been made (and the choke cap reassembled), start the vehicle and

observe how the vehicle performs for the first thirty to sixty seconds:

If the choke plate refuses to move at all when the engine first fires, there may be a number of

reasons:

o the cork seal is installed in between the main body and housing may be missing,

o the hot air supply may be blocked with carbon, or a lead ball,

o the linkages or the piston could be binding, or

o the vehicle may have a very, very lumpy cam and make insufficient vacuum to move

the pull-off piston.

If the engine is running overly rich (black smoke, strong smell of unburnt fuel, or rich-stalls), adjust

the choke pull-off to open the choke plate a tiny bit more.

If the engine hesitates, backfires or lean-stalls, adjust the choke pull-off to close the choke blade

a tiny bit more

Be careful, as a tiny change in the choke pull-off is amplified by the linkage and makes a big

difference to the choke plate position.

b) Adjusting how long it takes the choke to start opening once the

engine has fired.

The choke plate should be tightly shut when the engine is cold.

With either of the hot-air or electric chokes, start the choke coil

adjustment by turning the mark on the choke coil to the index

position on the housing. To adjust the choke coil, start the vehicle

and let it run for thirty to sixty seconds.

If the engine hesitates, backfires or stalls after the thirty to sixty

seconds, the choke is probably opening too soon. Loosen the

three lock screws (see red arrows in the image above) and turn the choke cap one index mark

anticlockwise (RICHER). Tighten the three lock screws, let the engine cool all the way down then

repeat the tuning.

If the engine is running very rich (black smoke or the smell of unburnt fuel) after the thirty to sixty

seconds, the choke is probably opening too late. Loosen the three lock screws and turn the choke

cap one index mark clockwise (LEANER). Tighten the three lock screws, let the engine cool all

the way down then repeat the tuning.

If the choke plate won’t open all the way even long after the engine has warmed up, the problem

issue is almost certainly a lack of heat to the choke coil - blocked exhaust crossovers, missing or

defective heat riser valves, blown electrical fuses or blown electric coil.

c) Adjusting the unloader tang.

When the engine is cold and the choke is closed, check that the

fast idle cam is on the highest step. Push the accelerator slowly to

the floor. The choke plate should be observed to be mechanically

forced open at least as much as the choke pull-off would open it

(about 11

/32”). Although not critical, the amount that the choke is

forced open can be adjusted by bending the unloader tang. The

tang is pretty heavy, and buried under all the fast-idle linkages – it

is easier to remove the choke housing first before bending the

unloader tang. The image to the right shows the fast idle screw

(item 1) and the unloading tang (item 2). Bending the unloader tang in the direction of the green

arrow will crack open the choke plate more.

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11.4 Power Valve Blowout Preventer (Check Ball).

It is possible to damage the power valve diaphragm by

engine backfire. For carburettor built after 1992, a power

valve blow-out protection system (a ball check valve is

located in the throttle body, designed to be normally open

but which quickly seats to close off the internal vacuum

passage when a backfire occurs) is installed. Once

closed, the check valve interrupts the pressure wave

caused by the backfire, thus protecting the power valve

diaphragm. A kit (part number 125-500) is available to

retrofit the power valve blow-out protection system to pre-

1992 350 Holleys. The kit contains a drill bit with stop

collar, two check balls, springs and retainers and is installed with the carburettor removed from the

vehicle and the throttle plate removed from the main body. Note that two balls/stops/retainers are

supplied as the kit is also used on four-barrel carburettors with secondary power valves. To install the kit:

1. Clamp the throttle body gently in a drill press, using soft faces to protect the aluminum.

2. Check that the stop collar is mounted 0.300” from the supplied drill tip and is tight.

3. Locate the power valve passage on the top face of the throttle body (circled in red in the image to the right). Drill the passage larger, until the stop collar contacts the throttle body.

4. Remove the throttle body from the drill press and blow out all passages with compressed air to remove any drill chips.

5. Install the spring (tapered side facing up) into the newly drilled power valve passage, followed by the check ball.

6. Tap the spring retainer into place, flush with the surface of the throttle body.

11.5 Better Fuel Metering (Adjustable Metering Block)

An adjustable metering block is available for 350 Holley carburettors (Holley part number 134-276),

identified by the numbers "12323" stamped into the casting on its throttle lever side. The metering block is

supplied with all Keith Dorton Signature Series 350CFM carburettors, and is used to tune the fuel curve to

individual vehicles. Gains of 5-7HP have been reported when the block is used instead of the factory

metering block. The adjustable metering block has the following features:

The factory 350 Holley metering block doesn't have emulsion tube holes drilled in to the main well.

Common practice is to drill different sized holes in the main well chanels to get the engine to operate

at around 12.5:1 air/fuel ratio throughout its power curve. The holes introduce air in different volume

amounts (controlled by the number of bleed holes and

their diameter), and at different points in the fuel curve

(controlled by their vertical placement in the channel).

However, once the holes are drilled, they cannot be

readily “undrilled”. The adjustable metering block has

five screw-in emulsion air bleeds for the main circuit.

These are supplied as 0.031”, 0.031”, 0.031”, 0.020” and

0.020” (bottom to top).

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Similarly, the factory 350 Holley metering block power valve restriction channels (PVCRs) are not

adjustable. Common practice is to drill out the PVCRs larger than the factory size (~0.056”). Again,

once the PVCRs are drilled, they are difficult to “undrill”. The adjustable metering block has screw-in

PVCRs, supplied at 0.042”.

At wide-open throttle (WOT), the high vacuum generated in t

he venturis can suck unmetered fuel from the accelerator

pump discharge nozzles. The adjustable metering block has

an anti-siphon air bleed fitted in the accelerator pump passage

just above the main metering jets (sometimes referred to as a

“kill bleed”). The bleed is supplied with a 0.020” screw-in

restriction. Air introduced into the pump passage by the bleed

breaks the vacuum being pulled on the fuel, and stops the

accelerator pump feeding the mixture at WOT.

A wide range of screw-on restrictions are available to tune the

emulsion air bleeds, PVCRs and kill bleed as per the table below:

Part Number

Hole Size

Part Number

Hole Size

Part Number

Hole Size

Part Number

Hole Size

142-00 Blank 142-29 0.0292” 142-39 0.039” 142-59 0.0595”

142-20 0.020” 142-31 0.031” 142-40 0.040” 142-62 0.0625”

142-21 0.021” 142-32 0.032” 142-41 0.041” 142-64 0.0635”

142-22 0.0225” 142-33 0.033” 142-42 0.042” 142-67 0.067”

142-24 0.024” 142-35 0.035” 142-43 0.043” 142-70 0.070”

142-25 0.025” 142-36 0.036” 142-46 0.0465” 142-73 0.073”

142-26 0.026” 142-37 0.037” 142-52 0.052” 142-76 0.076”

142-28 0.028” 142-38 0.038” 142-55 0.055” 142-78 0.078”

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12 Contacts

Holley

Dealers:

http://www.holley.com/dealers/InternationalHolleyDeal

erLocator.asp

Email: http://www.holley.com/TechService/TechRequest.asp

Internet: www.holley.com

AussieSpeed Performance Products

Address: PO Box 4009 Seaton, SA 5023 Australia

Telephone: (04) 03221105

Internet: www.aussiespeed.com

Redline Performance (Hardiman Auto Supplies)

Address: 9 Bullecourt Avenue Milperra, NSW 2214 Australia

Telephone: (02) 87238888

Facsimile: (02) 97712176

Email: [email protected]

Internet: www.redlineauto.com.au

K&N

Dealers: http://www.knfilters.com/search/dealersearch.aspx

Email: [email protected]

Internet: http://www.knfilters.com.au

http://www.holley.com/dealers/InternationalHolleyDealerLocator.asp

http://www.holley.com/dealers/InternationalHolleyDealerLocator.asp

http://www.holley.com/TechService/TechRequest.asp

http://www.holley.com/

http://www.aussiespeed.com/

mailto:[email protected]

http://www.redlineauto.com.au/

http://www.knfilters.com/search/dealersearch.aspx

mailto:[email protected]

http://www.knfilters.com.au/

FB/EK Holden Holley 350 Guide

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