Evaporative Emissions System: Description and Operation

Fig. 1 Air injection system:

Fig. 3 Evaporative emission control system:

This system, Figs. 3 and 1, prevents fuel vapors from escaping into the atmosphere. This system collects fuel vapors from the fuel tank and carburetor float bowl, and stores them in a charcoal canister. Vacuum is applied to the charcoal canister when the engine is operating. This draws the vapors from the trap into the engine and is mixed with the air intake charge and are burned in the combustion chambers.

Fig. 4 Evaporative emission control system fuel vapor flow:

OPERATION

When the engine is not operating, the float bowl vent valve opens, Fig. 4. The fuel vapors from the carburetor and the fuel tank collect in the canister.
When the engine is operating, the float bowl vent valve closes and engine vacuum is applied to the charcoal canister. This draws ambient air through the purge valve, canister and canister purge line to the carburetor assembly.