Each Mini Bike uses a specific engine. Each engine has to have a return spring on the throttle control to return to idle once you let off of the pedal. The best engines to use on Mini Bikes are Tecumseh and Robin. Each of these companies make certain models of engines specifically for Mini bikes. Height is a concern on most frames as it generally will not allow the larger engines to be used in them. We do not recommend Briggs and Stratton engines for mini bikes since they will not honor any warranty on engines used on mini bikes.
