Bill,
Is it hand crank or electric start? If hand crank, turn the engine over slowly and listen for a fairly loud click that indicates the mag's impulse coupling has tripped. It will come from the mag area. If no click, the impulse coupling will have to be repaired. If it does click, try cleaning the points in the mag with some alcohol and a new dollar bill. Then polish the points with a piece of hard writing paper (dry). If the points have oxidized, this should get them to make good contact again. If none of this works, let us know and I'm sure someone can give you further pointers. Of course, you could always drag the tractor to a shop and pay someone to fix it, but that's not as much fun. :o)
Phil
