Abstract: A carburetor air injection system comprising a downdraft carburetor which includes a butterfly type automatic choke valve, a butterfly type throttle valve spaced from said automatic choke valve, an idler jet in the carburetor on the opposite side of the throttle valve from the automatic choke valve, and a fuel jet between the automatic choke valve and the throttle valve. An air injector plate is positioned between the carburetor and the intake manifold. The air injection plate includes capillary air orifices feeding constantly controlled quantities of air into the air-fuel mixture passing from the carburetor to the intake manifold during operation of the engine. A flexible tubing having an air filter removably associated therewith is connected to the air injector plate.