Fuel Evaporation System: Operation
When engine is not running, fuel vapor from tank vents through check and relief valve into crankcase on I-Mark and into canister on P'UP and Trooper II. Ventilation valve (I-Mark) and vent switching valve open and carburetor vapor vents into canister. Purge control valve is closed.
When engine is running, vent switching valve closes by solenoid action. Ventilation valve (I-Mark) closes when manifold vacuum reaches 2.4-2.8 in. Hg. Any vacuum in fuel tank or crankcase (I-Mark) exceeding .2-.6 in. Hg will open relief side of check and relief valve to atmosphere. Purge control valve opens by distributor's vacuum advance signal and allows canister vapors to be drawn into intake manifold.