The function of the choke plate is to restrict the air flow into the carburetor, which causes a higher vacuum on the discharge ozzle, giving a richer mixture for starting purposes. A small movement in the choke plate causes a great change in the fuel air mixture.

The relief valve opens and then closes automatically, depending on engine load and speed. When the engine reaches normal operating temperature, the choke plate must be fully open to assure maximum power and economy from the engine.