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Gaseous and PM emissions of three Class 1 (sub-170 cc) on-highway motorcycles from Thailand that were equipped with crankcase scavenged two-stroke engines were evaluated at the U.S. EPA-National Vehicle and Fuel Emission Laboratory (NVFEL). Very little data currently exists on PM emissions from two stroke motorcycles. There are a large number of two stroke motorcycles in Asia, which appear to be a considerable contributor to PM inventories. This testing was conducted in response to a request from the World Bank for assistance in determining emissions factors for motorcycles commonly used in Asia.

In the 1990's there will be a different mix of vehicle technologies than existed in the late 1970's when inspection/Maintenance (I/M) programs were first mandated. These changes include the widespread use of “closed-loop” computer control of engine parameters and fuel injection. Several studies by EPA are examined to determine the effect of these changes on existing I/M programs and to investigate new methods of vehicle inspection. The report discusses the effectiveness of a standard idle emission test versus other inspection methods, the role of proper preconditioning, self-diagnostic trouble code checks as a method to identify high emitting vehicles, uncertainties in predicting tampering and misfueling rates for the future, problems with decentralized programs, and the effectiveness of I/M repairs in reducing vehicle emissions as measured on the Federal Test Procedure.