Any improvements of the fuel economy with engines are always required for all petroleum fuel vehicles. Such improvements often accompany some changes of the engine characteristics. It may cause slight disharmony with driving performances of the acceleration and/or top speed. The riding feelings on the motorcycles are so sensitive that means of changes for engine characteristics are limited to maintain good response in transition. We have developed the strong hybrid motorcycle "HV-X." It consists of a 4-stroke 250 cm₃ a cylinder engine and two 300V AC motors with a planetary gear set. Though the engine comes from a conventional scooter, utilizing the electric power, the HV-X attains better fuel economy without severe influence onto the drive performance even the engine character changes.