Abstract: An apparatus for increasing the efficiency of carburetors for internal combustion engines comprises a base having an opening for the passage of the fuel mixture from the carburetor and having a cavity for controlledly admitting secondary air towards said opening, through a plurality of conduits extending within the opening, a first grid partially spanning the throat of the carburetor and a second grid partially spanning the opening at the level of the surface of the base which engages the admission manifold of the engine, such that a non-obstructed gap is left between said grids at the opening. Also, a filter is provided in said cavity, said filter having control valves for admitting air into said cavity, said valves being adjustable for controlling the amount of air to be admitted into the opening.