Carburetor Fuel Bowl Thermal Vent Valve

Fig. 10 Carburetor fuel bowl thermal vent valve:

The thermal vent valve, Fig. 10, used on some vehicles, is a temperature actuated on/off valve, that is inserted in the carburetor to carbon canister vent line. This valve is closed when the engine compartment is cold, preventing fuel tank vapors, generated when the fuel tank heats up before the engine compartment, from being vented through the carburetor bowl.