Thanks to its lightness, small dimensions and attractive simplicity, the two-stroke, S.I. engine may be potentially preferable to the four-stroke one for city cars and other small vehicles. However, the loss of fresh mixture from the exhaust port, together with bad combustion and/or misfire at light loads constitute great limitations. Our researches directed to solve these problems concern the development of an air-assisted, low-pressure, pumpless injection systems, which bypasses the trapping losses, and the solution of combustion problems at light loads by means of charge stratification and innovative ignition systems.