Fuel Evaporation System: Operation

Fuel vapors are vented through an orifice vapor separator assembly in top of fuel tank. Vapors then leave separator through a single vapor line, and continue to the carbon canister in engine compartment. The vapors are absorbed by carbon granules until they are purged from canister by carburetor/throttle body vacuum once engine is started.

FUEL FILLER CAP  : Fuel filler cap has one-way vent. This prevents tank collapse, by allowing air to enter tank as fuel is consumed.

FUEL TANK  : In most installations, fuel tank is constructed with dome in top. Fuel vapors rise and gather in this dome.

ORIFICE VALVE  : On all vehicles, liquid fuel is prevented from entering vapor lines by restricted orifices. Orifices usually are a .050" (1.27 mm) orifice valve, located in emission control valve in fuel tank dome.

CARBON CANISTER  : Carbon-filled canister acts as storage system for fuel vapors vented from fuel tank and carburetor/throttle body. Outlet of canister is connected to carburetor/throttle body bowl vent.