Evaporative Emissions System: Description and Operation

Description
The evaporative emission control system is used to reduce hydrocarbons emitted to the atmosphere from the fuel system. The reduction of hydro carbons is accomplished by activated charcoals in the carbon canister.

OPERATION
At engine stop
Fuel vapor from the sealed fuel tank is led into the carbon canister which is filled with activated carbon and stored there.
The vapor in the carburetor float chamber is also led into the canister through the outer vent pipe because the vent switching valve is normal IV open.

During engine operation
The canister retains the vapor until the canister is cleaned by air drawn through the purge line to the intake manifold.
As engine speed increases, the ported vacuum rises and purge control valve opens the orifice allowing the vapor to travel through the purge line to the intake manifold.
When the engine coolant temperature is lower than 60°C (140°F), the purge control valve closes by the movement of the solenoid valve. This prevents vapor from flowing into the intake manifold. Evaporative purge control valve is installed in the purge line in place of purge orifice. The purge control valve controls the flow of purge air in proportion to intake air quantity.