Closing the choke plate when starting a cold engine restricts the air entering the carburetor through the air cleaner and creates an increase in suction at the jets. This increase in suction causes more fuel to be drawn into the engine and provides a richer mixture for starting a cold engine. As soon as the engine starts, a poppet valve in the choke plate automatically opens and admits sufficient air to avoid over-choking or flooding of the engine. As the engine warms, the choke plate must be gradually returned to the open position.