Fuel Evaporation System: Operation
When fuel tank pressure exceeds a preset value, two-way valve opens and allows excess vapors to vent into canister. If excessive vacuum forms in fuel tank, two-way valve opens and outside air enters fuel tank through canister. Fuel filler cap acts as a safety valve if evaporation system fails.
Thermovalve closes and allows manifold vacuum to open purge control valve when engine coolant temperature exceeds set temperature.
When engine is not running, air vent cut-off valve closes float bowl vent to secondary bore and opens vapor vent to canister. When engine is running, manifold vacuum opens air vent cut-off valve to secondary bore and closes off vent to canister. Vacuum holding solenoid stabilizes vacuum on air vent cut-off diaphragm.
When engine is not running on Prelude, air vent cut-off solenoid valve opens outer air vent passage. This allows float bowl vapors to vent into canister. When engine is running above 500 RPM, air vent cut-off solenoid valve and inner vent solenoid valve open float bowl inner and sub-inner air vent passages to air cleaner. On hot engine starts, when coolant temperature is above 158°F (70°C), delay timer delays opening of inner air vent passage to ease hot engine start up.
When engine is not running, fuel cut-off solenoid valve shuts off main and slow primary fuel metering passages to carburetor bore. On Accord, when ignition key is off, power valve fuel passage to carburetor bore is closed by power valve control solenoid and check valve.