Evaporative Emission Control Canister: Description and Operation

The charcoal canister is used to store fuel vapors from the carburetor and fuel tank when the engine is not operating. A purge control valve, which is activated by the distributor vacuum advance diaphragm signal after the engine has been started, is closed when the engine is not operating to prevent fuel vapors from flowing to the intake manifold. When the vacuum signal exceeds a specified value, the purge control valve opens and allows fuel vapors to be drawn from the canister to the intake manifold.