Evaporative Emissions System: Operation
When gasoline and vapor in fuel tank expand, they force open the 2-way valve. Liquid fuel is separated and returned to tank, while vapors pass to canister and are absorbed by charcoal filter. Excess air is vented to atmosphere.
When engine is started, primary main fuel cut-off solenoid valve opens, allowing manifold vacuum to purge control valve and vacuum holding solenoid valve. Vacuum is sent to air vent cut-off diaphragm so it will open and vent float bowls. When engine is warm, thermovalve opens and operates purge control diaphragm valve; vacuum flows to canister purge diaphragm and air is drawn through to purge canister. See Fig 1.