The 400 ASi's power arrives via a fuel-injected 376cc single cylinder air/oil cooled four-valve power plant. The fuel injection was outstanding. The 400 ASi started effortlessly, even at 10,000 feet with temperatures hovering in the high 30s. Although peak power inevitably suffers at such altitudes, the fuel injection managed the air/fuel calibration, compensating for altitude and temperature changes automatically. The engine power is certainly sufficient for trail riding or handling a hard day of work, but falls shy of some other 400-class machines.