Evaporative Emissions System: Description and Operation

This system is used to prevent fuel vapors emitted from the fuel tank and carburetor from escaping into the atmosphere. This is accomplished through the use of a non-vented fuel tank, a special fuel filler cap, charcoal canister (some applications), vapor separators check valves, non-vented carburetor, and hoses necessary to connect these components together.

On early models without a charcoal canister, the system routes the fuel vapors from the tank, through a check valve and connecting lines to the valve cover. When the engine is started, the fuel vapors are drawn in through the PCV system and burned a long with the normal air fuel mixture.

On later models with a charcoal canister, the fuel vapors are absorbed and stored in the charcoal canister until the engine is started. These vapors are then drawn either through the air cleaner snorkel or through a ported vacuum port in the carburetor (depending on application) and burned along with the normal air fuel mixture