Exhaust Emissions System - EVAP: Operation

Fuel vapor is stored in expansion chamber in fuel tank and in vapor line up to two-way valve. When vapor pressure becomes higher than set pressure of two-way valve, valve opens allowing vapor into charcoal canister. When vacuum exceeds set pressure of one-way valve or two-way valve, valve opens and air is drawn through charcoal canister into fuel tank.

When engine is stopped, purge control solenoid valve is closed and fuel vapor is absorbed by charcoal. When ignition switch is turned on, the solenoid valve opens, allowing stored vapors to enter carburetor as carburetor vacuum increases.

The vacuum-operated carburetor vent valves close when engine is turned off, directing fuel vapor in float chambers into the charcoal canister. Any excessive pressure or vacuum build-up is relieved by valves in the filler cap.