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A gaseous fuel emission control system which includes a three-way catalyst for the after treatment of exhaust gases has been developed for a 398 cc, four-stroke, air-cooled, spark ignition, overhead valve utility engine. The fuel delivery system utilized analog closed-loop air/fuel ratio control to maintain a narrow operating band about the stoichiometric air/fuel ratio. Using liquified petroleum gas (LPG) as the fuel, carbon monoxide emissions tested per CARB modal weighting factors were reduced by 98% and HC + NOx were reduced 62%. The emission levels were below the CARB 1995 Iimits. The emission control system shows considerable promise for controlling carbon monoxide emissions for indoor applications. The system was developed for gaseous fuels only where the engine can be run at the stoichiometric air/fuel ratio.