Holden HQ–HZ Hard Starting Problems - Causes and Remedies

Hard Starting of Holden HQ–HZ Engines

Hard starting in Holden HQ–HZ models can be frustrating, especially when the engine cranks but refuses to fire. These classic Holdens rely on a combination of proper ignition, fuel delivery, and mechanical condition to start smoothly. Below is a detailed guide to diagnosing and fixing common causes.

Slow Cranking

When the engine turns over slowly, check the following:

Heavy engine oil
• Change to the correct grade for your climate and engine condition
Partially discharged battery
• Charge battery fully before testing
Poor battery connections
• Clean terminals and tighten or replace corroded connectors
Faulty ignition‑starter switch
• Replace switch if intermittent or non‑responsive
Faulty starting motor or drive
• Overhaul or replace starter motor
Faulty battery
• Replace with a battery of correct capacity and cold‑cranking amps

Ignition Trouble

If the engine cranks but fails to fire, ignition faults are often to blame:

Distributor points burned or corroded
• Clean or replace points
Points incorrectly adjusted
• Set correct gap and dwell angle
Spark plugs incorrectly gapped
• Adjust plug gap to specification
Spark plug wires loose or corroded in distributor cap
• Clean terminals and ensure tight fit
Loose connections in primary circuit
• Tighten all connections
Series resistance in condenser circuit
• Clean all connections
Low‑capacity condenser
• Install condenser of correct rating
Ballast resistance faulty or out of circuit
• Inspect and correct wiring or replace resistor

Engine Condition

Mechanical issues can also cause hard starting:

Valves holding open
• Free up valves and check for sticking
Burnt valves
• Grind or replace valves
Leaking manifold gasket
• Tighten manifold bolts or replace gasket
Loose carburettor mounting
• Tighten carburettor base nuts
Faulty pistons, rings, or cylinders
• Poor compression — overhaul engine if necessary

Carburetion Problems

Fuel delivery faults are common in older Holden engines:

Choke not operating correctly
• Adjust or repair choke mechanism
• Check air cleaner position
Throttle not set correctly
• Adjust throttle linkage
Carburettor dirty or passages restricted
• Overhaul and clean carburettor
Fuel pump output low
• Overhaul or replace fuel pump

Rochester Quadrajet Carburettor

Problem: Engine cranks but will not start or starts hard.
Possible Causes & Remedies:

Choke operation
• Check choke system for proper movement
Needle valve sticking or clogged vacuum hose
• Inspect float and needle valve
Fuel cut solenoid valve not opening
• Test and replace solenoid if faulty

Insufficient fuel supply to carburettor:

Fuel filter clogged
• Replace filter
Fuel pump faulty
• Replace pump
Fuel line clogged
• Clean or replace line
Fuel line bent or kinked
• Replace damaged section

Stromberg Carburettor

Problem: Engine cranks but will not start or starts hard.
Possible Causes & Remedies:

Choke operation
• Check choke system
Needle valve sticking or clogged vacuum hose
• Inspect float and needle valve
Fuel cut solenoid valve not opening
• Check solenoid valve and wiring

Final Thoughts

Hard starting in Holden HQ–HZ engines is usually caused by simple issues — poor electrical connections, incorrect choke operation, or fuel delivery faults. Regular maintenance and proper adjustment of ignition and carburettor components will keep these classic Holdens starting easily and running reliably.

While this guide helps trouble shoot common problems of the Holden HQ-HZ engines the Holden HQ-HZ 1971-1978 Workshop Manuals available from Car Manuals Direct includes all the original specifications, adjustment, torque settings and repair procedures used by Holden mechanics.

Safety, Copyright and Source Notice

Safety Disclaimer
Working on motor vehicles involves hazards. Always follow correct procedures and consult a qualified technician.

Source
Information compiled from period factory service literature.

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