This is a temperature controlled device that improves warm engine performance and reduces carburetor icing. The air filter assembly is equipped with a vacuum controlled intake airflow control diaphragm and a bimetal air inlet valve inside the air filter. The air inlet valve is closed when the temperature of the air to be cleaned is less than 25°C, thereby allowing manifold vacuum to open the air control diaphragm and supply heated air to the carburetor. If a vacuum at a higher temperature is detected at the control air diaphragm inlet and air leaks out, the valve is defective and must be replaced. When checking this system, make sure that the hot air pipe is connected to the base of the intake duct and the other end is connected to the exhaust pipe. Fresh air is heated by blowing the exhaust pipe and enters the carburetor through a hose.
Very often, the hose is disconnected when the air filter is removed and then passed through when installed. This causes problems when driving the car in cold conditions.