The 1949-69 Volkswagen models do not utilize an evaporative emission control system. 1970-81 models do utilize this system. A description of the 1970-81 evaporation emission control system will be presented here to provide further general automotive understanding of emission systems.
The evaporative emission control system prevents fuel vapors from escaping into the atmosphere from the fuel tank. The fuel tank is vented to a system which contains fuel vapors until they can be burned by the engine.
The fuel tank is attached to an overflow chamber via a fuel hose. Liquid gasoline can be temporarily stored in this chamber when the fuel level in the fuel tank rises due to expansion. When the gasoline level in the fuel tank decreases, the gasoline stored in the overflow chamber can drain back into the fuel tank.
Fuel vapors can escape from the overflow chamber through a fuel hose to an activated charcoal (EVAP) canister located under one of the rear fenders. The charcoal in the EVAP canister absorbs the fuel vapors so that they do not vent into the atmosphere. When the engine is started, air is forced through the EVAP canister by the engine cooling fan. The fuel vapor from the canister passes through a hose into the air cleaner, where it mixes with the incoming air charge to be burned in the engine.
None of the 1949-69 Volkswagen vehicles are equipped with this system; this description is only for general information on exhaust emission controls used on 1970-81 models.