Canister Purge Control Valve: Description and Operation

The electrically operated vent switching valve is built into the carburetor. When the engine is operating, the vent switching valve is closed to prevent ambient air from entering the carburetor through the charcoal canister. When the engine is not operating, the vent switching valve is opened to permit fuel vapors from the carburetor to flow to the charcoal canister where they are stored until the engine is started.