Abstract: A supplementary fuel injection apparatus for an internal combustion engine comprising a pressure type fuel reservoir member having pressure supplied by the engine exhaust gas, a chambered fuel pump and metering regulator member tubularly connected to said reservoir and having a fuel chamber and a vacuum chamber, a diaphragm therebetween, diaphragm fuel pump means in said vacuum chamber that is power actuated by vacuum pressure supplied from the engine intake manifold, and a fuel distribution unit having a fuel passage connected to said fuel pump and metering regulator unit and the carburetor of the said engine and said unit having a fuel control means therealong and a variable fuel pressure metering means mounted on the carburetor adjacent the venturi thereof.