See Figures 1, 2 and 3
When raw fuel evaporates, the vapors contain hydrocarbons. To prevent these fumes from escaping into the atmosphere, the fuel evaporative emission control system was developed.
The system consists of a sealed fuel tank, a vapor/liquid separator (certain models only), a vapor vent line, a carbon canister, a vacuum signal line and a canister purge line.
In operation, fuel vapors and/or liquid are routed to the liquid/vapor separator or check valve where liquid fuel is directed back into the fuel tank as fuel vapors flow into the charcoal filled canister. The charcoal absorbs and stores the fuel vapors when the engine is not running or is at idle. When the throttle valves in the carburetor (or air intakes for fuel injection) are opened, vacuum from above the throttle valves is routed through a vacuum signal line to the purge control valve on the canister. The control valve opens and allows the fuel vapors to be drawn from the canister through a purge line and into the intake manifold and the combustion chambers.
INSPECTION AND SERVICE
Check the hoses for proper connections and damage. Replace as necessary. Check the vapor separator tank for fuel leaks, distortion and dents, and replace as necessary.Carbon Canister and Purge Control Valve
To check the operation of the carbon canister purge control valve, disconnect the rubber hose between the canister control valve and the T-fitting, at the T-fitting. Apply vacuum to the hose leading to the control valve. The vacuum condition should be maintained indefinitely. If the control valve leaks, remove the top cover of the valve and check for a dislocated or cracked diaphragm. If the diaphragm is damaged, a repair kit containing a new diaphragm, retainer, and spring is available and should be installed or replace the carbon canister assembly.
REMOVAL & INSTALLATION
Removal and installation of the various evaporative emission control system components consists of disconnecting the hoses, loosening retaining screws, and remove the part which is to be replaced or checked. Install in the reverse order. When replacing hose, make sure that it is fuel and vapor resistant type hose.