Float Bowl
When engine is not running on Prelude models, air vent cut-off solenoid valve closes float bowl vent to air cleaner and opens vapor vent to canister. This allows expanding float bowl vapor to be vented to canister. When engine is running (greater than 400 RPM), ECU energizes air vent cut-off solenoid valve, opening passage between air cleaner and float bowl and closing off vent to canister.
On Accord models, an air vent cut-off diaphragm opens float bowl to canister when ignition is off. When ignition is on, vacuum holding solenoid is energized. This causes manifold vacuum to activate vent cut-off diaphragm, closing off float bowl to canister and opening float bowl to air cleaner. Vent passage to canister is also regulated by a thermovalve built into carburetor. This valve will restrict vapor flow to canister until temperature exceeds 91°F (33°C).