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In response to a growing need for a practical and technically valid method for measuring exhaust sound pressure levels (SPL) of on-highway motorcycles, the SAE Motorcycle Technical Steering Committee has developed Surface Vehicle Recommended Practice J28251, “Measurement of Exhaust Sound Pressure Levels of Stationary On-Highway Motorcycles,” which includes a new stationary sound test procedure and recommendations for limit values. Key goals of the development process included: minimal equipment requirements, ease of implementation by non-technical personnel, and consistency with the federal EPA requirements; in particular, vehicles compliant with the EPA requirements should not fail when assessed using J2825. Development of the recommended practice involved a comprehensive field study of 25 motorcycles and 76 different exhaust systems, ranging from relatively quiet OEM systems to unbaffled, aftermarket exhaust systems.

Comparison of before-repair and after-repair test results for approximately 800 1981 and later model cars and light trucks recruited from customer service shows that the primary cause of excessive emissions depends on fuel metering technology (i.e., carburetor versus fuel-injection). With carbureted vehicles, mechanical component failure is the largest contributor to excessive emissions. Specifically, the need for adjustment or other repair of the carburetor is the single greatest cause of excessive emissions for carburetor-equipped vehicles. Ignition system maintenance and oxygen sensor replacement are the next most significant items. Electrical component failure is the largest source of excessive emissions for fuel-injected vehicles. Oxygen sensor failure is the single greatest source of excessive emissions and ignition system problems are second largest emissions source.

Programs to control motor vehicle emissions originated in California as a result of Professor A.J. Haagen-Smit of the California Institute of Technology discovering that two invisible automobile emissions, hydrocarbons and oxides of nitrogen, react together in the presence of sunlight to form oxidants such as ozone, a principal ingredient of the infamous Los Angeles area “smog”. The State of California became the first government to regulate the emissions of new automobiles when it adopted requirements for the use of positive crankcase ventilation (PCV) valves beginning with the 1963 model year.