Evaporative Emissions System: Description and Operation

Evaporative Emissions Control System:

The main component of the evaporative emission control system is the charcoal canister storage container. The fuel vapors from the fuel tank and carburetor float bowl are vented to the canister when the engine is not running. With the engine running during certain operating conditions the stored vapors are purged by intake air flow. Air enters the canister through a filter at the bottom. It mixes with the stored vapors and is drawn into the engine for combustion.

Type 1 Canister Control Valve Or bowl Vent Valve:

On some applications the canister control valve also operates a carburetor bowl vent valve.

The ECM controls system operation by opening a solenoid in the canister purge hose.

A thermal bowl bent valve is located in-line in the hose between the carburetor bowl vent and bowl vent valve. The thermal bowl vent valve closes at approximately 90 to 120 degrees. It opens at hotter temperatures and allows vapors to the canister control valve.