You need the matching flywheel that has the magnets in it to work. I think there was some electric start 5 hp that had them on you would have to find out from a parts dealer. take the model # and see what you can find out. But finding a used would not be easy and ne would be coast a lot. They put out about 15 amps and maybe you could fit a 8hp one on,there were a lot of older riders that had them on. Need the rectifier with it............Curt
PS the 5 and 8hp are the same size