Closing the choke plate when started a cold engine restricts the entrance of air to the carburetor and creates an increase in suction on the jets. The increase in suction causes more fuel to be drawn into the engine to provide the richer mixture needed for starting a cold engine. As soon as the engine begins to fire, the choke must be partially opened to prevent overchoking or flooding of the engine. As the engine warms up, the choke must be gradually opened to full open position.