Seven motorcycles, ranging in size from 100 to 1200 cm3, were tested for emissions characterization purposes. They were operated on the federal seven-mode test procedure (for 1971 and older light-duty vehicles), the federal LA-4 test procedure (for 1972 and later LDVs), and under a variety of steady-state conditions. Four of the machines tested had 4-stroke engines, and the other three had 2-stroke engines.
Emissions which were measured included hydrocarbons, CO, CO2, NO, NOx, O2, aldehydes, light hydrocarbons, particulates, and smoke. Emissions of SOx were estimated on the basis of fuel consumed, and evaporative hydrocarbon losses were also estimated. Crankcase “blowby” emissions from one 4-stroke machine were measured.
The impact of motorcycles on national pollutant totals was estimated, based on the test results and information from a variety of sources on national population and usage of motorcycles. In addition, a brief overview of emission control technology which might be applicable to motorcycles is presented. This discussion indicates that control of hydrocarbon emissions from 2-stroke machines and CO emissions from large motorcycles of both 2-stroke and 4-stroke types are immediate priorities for meeting the tentative 1976 EPA motorcycle emission standards.