Abstract: A valve is connected to an inlet opening on the conduit means leading from the carburetor of an internal combustion engine assembly to the combustion chamber of the engine. The valve has an air inlet thereon, and is operable by a conventional pneumatic vacuum actuator in response to the rotational speed of the engine to admit additional air of combustion to the conduit means for blending with the fuel and air mixture flowing therethrough from the carburetor to the combustion chamber. The additional air of combustion, which is proportional to the engine speed, improves combustion within the engine and thereby increases fuel efficiency while minimizing the production of pollutants.