Small Engines (Lawn Mowers, etc.): Craftsman lawn tractor, sears craftsman lawn tractor, craftsman lawn tractor

Question
My Sears Craftsman lawn tractor with 21hp B&S engine will not re-start while the engine still warm after I shut it off.  It starts fine when cold and it runs without any problems.  But if I shut the engine off to refuel or change accessories it won't start again and I have to let it sit for a couple of hours before I can get it started.  I checked and the plugs do not spark for some reason.  There's obviously spark while the engine is running, but for some reason no spark when I attempt to re-start it after I shut it off.  Any ideas?

Answer
The only way to find out what is causing this is to get it to the point where there is no spark, and then do some diagnosis. Try disconnecting the ground from the coil, if there is no spark, the coil is bad. If there is spark, you have a safety switch or ignition switch problem.