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In contrast to motorcycles with 4-stroke engines, 2-stroke engine motorcycles produce very high hydrocarbon and carbon monoxide emissions. Compared to a 1976 automobile, such motorcycles produce as much hydrocarbon emissions as ten to twenty passenger cars. Modified automobile catalyst technology with the addition of an air pump is shown to be effective in reducing the hydrocarbon and carbon monoxide emissions by 75 - 85% after mileage accumulation of 12,000 miles; these tests are in progress and are being continued. In spite of the fact that current 2-stroke engine motorcycles run rich (no excess air) hydrocarbon emissions can be reduced by 35% and higher with aged catalyst systems without the addition of air. The mechanical durability of the catalytic systems is completely satisfactory. Present data indicate that catalyst system technology has been developed to meet proposed interim EPA emission standards for 2-stroke motorcycle engines.

Three-way conversion catalysts systems which provide control of three emission components - hydrocarbons, carbon monoxide, and oxides of nitrogen - generally require the use of closed-loop feedback control of the air/fuel metering system to provide a near stoichiometric exhaust gas composition. As an alternate fuel such as ethyl-alcohol is added to gasoline, the stoichiometric air/fuel ratio is altered. Conventional air/fuel metering systems do not compensate for this change. This paper studies the ability of the Volvo closed-loop control fuel injection system, now in use on vehicles in the United States, to maintain the stoichiometric air/fuel mixture needed for optimum emission control and to compensate for the change in fuel stoichiometry encountered in gasoline/alternate fuel mixtures. The system was found to have the ability to completely compensate for gasoline/ethyl alcohol mixtures up to 30% ethyl alcohol with no loss in emission control.