Evaporative Emissions System: Description and Operation

Fig. 8 Evaporative Emission Control Ssytem:

Fig. 9 Charcoal Canister:

In order to allow a maximum of 10% fuel expansion, the maximum fuel level is limited by the inclusion of an expansion tank, Fig. 8, located within the fuel tank. The fuel tank is vented through a system of vapor lines and a liquid/vapor separator to a charcoal canister, Fig. 9, located in the engine compartment.
The flow of vapor to the canister is controlled by a pressure/vacuum relief valve located in the fuel vapor vent line. The vapor absorbed in the canister is purged by the engine through a vacuum operated valve. The valve is controlled by vacuum signal taken at the throttle housing, just upstream of the throttle plates.
Canister purging is controlled by a thermal vacuum valve which does not allow purging until the coolant temperature is above 43°F.