Following an analysis of the state of the art,the typical values of emissions and fuel consumption of 2 and 4 stroke engined motorcycles, which comply with Federal Std. 1978 are examined. In view of a further reduction in emission levels, experimental results of an unconventional 2 stroke engine, with reduced losses of fuel mixture during scavenging are reported. Considerable fuel economy is obtained while the reduction in emissions, although less remarkable is not negligible: about 50% of unburned hydrocarbons and 75% of carbon monoxide as compared to a conventional 2 stroke engine of same performances. Fuel consumption, as resulting from tests, is competitive with 4 stroke engines at wide open throttle and quite better at partial loads. Finally, a different approach to emission regulations, based on a total index of pollution, is proposed. On this basis the considered engine, which offers remarkable improvements in energy economy while keeping the advantages of the conventional 2 stroke engine,may be better evaluated.