It is limited by the state of tune, how aerodynamic you are, your weight, etc. but it is about 86 mph. Since the Hondamatics were designed to attract new riders to the sport of Motorcycle riding, they reduced the power from the engine with a different cam and smaller carbs. So If you here some one insist on a higher speed for a 400, that is the ordinary model, most likely. The 400A is rated at about 27 HP, the standard CB400 twin is around 40 hp.