The fuel system used on HK, HT and HG Holden models was designed to provide dependable fuel delivery and smooth engine performance. Six-cylinder engines commonly used a Bendix-Stromberg carburetor, while V8 models used either Stromberg or Rochester carburetors depending on the engine and year. Fuel is delivered from a mechanical pump mounted on the engine and then metered through the carburetor using floats, jets, air bleeds and vacuum-controlled components. When these parts are correctly adjusted the engine starts easily, idles smoothly and accelerates cleanly, but wear, dirt or incorrect settings can quickly lead to running problems.
Excessive fuel consumption or incorrect fuel mixture
• Metering jet incorrect, damaged or worn
• Main discharge jet incorrectly seated
• High speed air bleeder blocked or oversized
• Power by-pass jet blocked or incorrect size
• Vacuum power piston worn or sticking
• Fuel level set incorrectly
• Float needle valve dirty, worn or binding
These problems often cause the engine to run either too rich or too lean, resulting in poor fuel economy, rough running and black exhaust smoke.
Engine misses or hesitates during acceleration
• Accelerator pump inlet or outlet ball valve not seating correctly
• Pump piston washer worn or damaged
• Accelerator pump duration spring faulty
• Pump nozzle blocked or incorrect size
• Pump discharge nozzle gasket leaking
• Accelerator pump channels obstructed
• Pump linkage worn or incorrectly installed
A faulty accelerator pump prevents the extra fuel charge needed during throttle movement, causing hesitation or misfire when accelerating.
Engine will not idle correctly
• Idle tube blocked or incorrect size
• Idle air bleed blocked
• Idle discharge holes blocked or damaged
• Throttle body wear allowing excess air leakage
• Idle needle incorrectly adjusted or worn
• Choke diaphragm leaking
• Vacuum power piston worn or sticking
• Fuel level incorrectly set
Idle problems often appear gradually as carburetor passages become restricted or adjustments move out of specification.
Hard starting – cold engine
• Choke valve shaft or linkage binding
• Incorrect choke adjustment
• Thermostat spring broken or incorrectly installed
• Choke kick diaphragm leaking
Cold starting problems usually occur when the choke mechanism does not close or operate correctly.
Hard starting – warm engine
• Choke linkage binding or worn
• Incorrect choke settings
• Thermostat cover loose or leaking
• Thermostat housing gasket leaking
Warm starting problems may also occur if the choke system remains partially engaged after the engine has reached operating temperature.
Fuel pump problems
• Broken rocker arm inside the fuel pump
• Weak or broken rocker arm spring
• Pump linkage worn or damaged
• Fuel pump diaphragm punctured or worn
• Fuel leakage from diaphragm flange
If the fuel pump cannot supply enough fuel to the carburetor the engine may stall, lose power under load or fail to start.
The fuel systems fitted to HK, HT and HG Holden engines are generally reliable, but many vehicles now on the road are more than fifty years old. Worn carburetor components, blocked passages and incorrect adjustments are therefore common causes of drivability issues.
While this guide helps identify common engine problems, the Holden workshop manuals available from Car Manuals Direct provide the original specifications, adjustment settings and repair procedures used by Holden mechanics when these vehicles were new.