The one-way clutch mechanism seen on bicycles, etc. greatly ease the load of riders at times of coasting or descending downhill. Their use on motor vehicles are restricted to some automatic drive four-wheeled vehicles with torque converters. There are neither any example of mass-produced motorcycle with one-way clutch between the engine and the drive system nor any reports of quantitative study on its impact on the performance of the vehicle including fuel economy. The present paper reports the results of experimental research on one-way clutch employed in the drive system, obtained for motorcycles having five kinds of two-cycle engines of different displacements. The test on fuel economy showed an improvement of 4 - 9%.