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.
A solenoid timer valve is used on all models (except Federal Hatchback STD and DL, Sedan DL and Hardtop DL) to delay purging of carbon canister when engine is started. The time delay will be 130 seconds for manual transmissions and 245 seconds for automatic transmissions.
The check valve (located between canister and intake manifold) closes when engine is stopped to prevent vapors from entering intake manifold and accumulating there.