Abstract: There is disclosed an insert for insertion between the carburetor and the firing chamber of the cylinders in an internal combustion engine. The insert comprises a cylindrical cup-like configuration having a plurality of rectangular apertures symmetrically positioned about the major sidewall and having a pattern of small apertures located on the bottom surface. First and second circular screen members are positioned within the insert to overlie the bottom surface, while a cylindrical screen member is positioned within the hollow of the insert to surround the major side surfaces containing the rectangular apertures.