Early Fuel Evaporation System: Operation

The heat control valve operation is controlled by a counterweight and a thermostatic spring which is sensitive to the ambient temperature around the exhaust manifold.

When engine temperature is low, the heat control valve counterweight rotates counterclockwise until it is stopped by a stopper pin mounted in the exhaust manifold. In this position the heat control valve is closed and exhaust gases are routed below the manifold stove to heat the air/fuel mixture.

As the engine temperature rises and the ambient temperature becomes high enough to actuate the thermostatic spring, the counterweight rotates clockwise until it is again stopped by the stopper pin. In this position the valve is fully open and the exhaust gases pass through the exhaust manifold without heating the manifold stove.