Abstract: A catalytic converter is mounted at the exhaust gas outlet of a muffler for a two or four-cycle internal combustion engine of the type having one or two cylinders such as those used for lawn and garden equipment. The catalytic converter is located exteriorly of the muffler body in the path of the exhaust gases for oxidizing and/or reducing exhaust gas components subsequent to their discharge from the muffler. Secondary air supply is provided upstream of the catalyst within the converter by mounting the catalytic converter to provide a gap between the converter and the muffler body. Alternately, secondary air is provided by at least one opening formed in the converter upstream of the catalyst which communicates between the interior of the converter and atmosphere.