Connect a vacuum gauge to distributor main diaphragm hose and another vacuum gauge to distributor sub-diaphragm hose. If equipped with high altitude compensation system (HAC), disconnect lower vacuum hose of HAC valve and connect it to intake manifold.
Check that coolant temperature is below 106°F (41°C). Start engine. Check that main diaphragm vacuum gauge indicates steady vacuum when engine is accelerated or running at idle.
Warm up engine to normal operating temperature. Check that main diaphragm vacuum gauge indicates zero at idle and high vacuum when engine is accelerated. Check that sub-diaphragm vacuum gauge indicates high vacuum and fluctuates when engine is accelerated from idle.
Remove distributor cap and rotor. Apply vacuum to diaphragms checking that vacuum advancer moves. Reinstall cap and rotor. If system performed as described, testing is complete. If not, check individual components as necessary.

Fig 1: Starlet Spark Control System

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

System Testing: Starlet