HAC Valve (Carbureted)

Visually check and clean HAC valve filter. Start engine and set at idle. Blow air into any of the 3 ports on top of HAC valve. If air exits filter, valve is open and in high altitude position. If air does not exit filter, valve is in low altitude position. High altitude is greater than 3930 feet and low altitude is less than 2570 feet. If valve functions properly, proceed to TIMING CHECK.