Mechanically Controlled Thermostatic

Fig. 1 Mechanically controlled thermostatic assembly:

Carburetor air temperature is thermostatically controlled by the air duct and valve assembly. Air from the engine compartment, or heated air from the shrouded exhaust manifold is supplied to the engine Fig. 1.
During the engine warm-up period when the air temperature entering the air duct is less than 105° F, the thermostat is in the retracted position and the air valve is held in the closed position by the air valve spring, thus shutting off the air from the engine compartment. Air is then drawn from the shroud at the exhaust manifold. As the temperature of the air passing the thermostat unit rises, the thermostat starts to open and pulls the air valve down. This allows cooler air from the engine compartment to enter the air cleaner. When the temperature of the air reaches 130° F, the air valve is in the open position so that only engine compartment air is allowed to enter the air cleaner.