Evaporative Emissions System: Operation

When engine is stopped, accumulated fuel vapors flow into charcoal canister through evaporation hose. When engine is idling, high manifold vacuum closes purge valve, trapping vapors in canister. As engine speed increases, carburetor vacuum overcomes manifold vacuum to open purge valve, allowing vapors to enter intake manifold.

The two-way valve (located in evaporation hose) controls the flow of fuel vapor from fuel tank to charcoal canister and the flow of fresh air into tank. The check valve (located between canister and intake manifold) closes when engine is stopped to prevent vapors from entering intake manifold and accumulating there.