System Tests: Pickup

If at high altitude, disconnect and plug hose at distributor sub-diaphragm. Ignition timing should be 8° BTDC. Reconnect hose - timing should advance 7°. Disconnect and plug vacuum hose located between vacuum pipe and check valve at vacuum pipe. Timing should not change for at least one minute.
Stop engine. Reconnect hose to check valve. Disconnect and blow through hoses on top of HAC valve. Air should pass freely through to carburetor. Reconnect hoses.
If at low altitude, ignition timing should be 8° BTDC. Disconnect and plug vacuum hose from lower port of HAC valve. Timing should advance 7°.

Fig 1: High Altitude Compensation System (Pickup)