1978 Models

Disconnect vacuum hose to distributor advance mechanism and attach vacuum gauge to hose. With engine cold, start and run engine at 2000 RPM. Vacuum gauge should indicate manifold vacuum.

Fig 1: 1975 Spark Delay System (2T-C Engine)
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On 2T-C engine, warm engine to normal operating temperature. Increase and maintain engine speed at 3000 RPM. Check that vacuum gauge reading changes from low to high within 3 seconds. Reconnect vacuum hose to distributor.
On 20R and 2F engines, pinch hose to carburetor port. Warm engine to normal operating temperature. Increase and maintain engine speed at 3000 RPM. Check that vacuum gauge reading changes from low to high within 3 seconds. Reconnect vacuum hose to distributor.
On all models, remove delay valve and blow through it. Air should flow in one direction only (toward colored side). Use cold/hot water to test thermal vacuum switch to determine it if allows passage of vacuum. When cold, vacuum should not pass. When hot, vacuum should pass.
Remove distributor cap and rotor dust cover. Apply vacuum to advance mechanism and check that distributor advance mechanism moves when vacuum is applied.