Land Cruiser

If at high altitude, disconnect and plug hose at distributor sub-diaphragm. Ignition timing should be 7° BTDC. Reconnect hose - timing should advance 5°. Disconnect and plug vacuum hose at black side of check valve. Timing should not change for at least one minute.
Stop engine and blow through hoses from HAC valve to carburetor. Air should pass freely. Remove check valve and see that air passes from white to black side, but not the other direction.
If at low altitude, ignition timing should be 7° BTDC. Pinch hose at HAC valve leading to distributor sub-diaphragm. Timing should advance.

Fig 1: High Altitude Compensation System (Land Cruiser)