Mike W:
There can be a number of reasons that a tractor quits running after warmup. Your number one clue is that it is OK after cooling off.
-If it cranks but won't start, cross seized engine off the list. If it cranks weird (like too fast) you've lost compression (see my last comment below).
- Check for spark as soon as it quits.. No spark, look at points, coil, condenser. Check to see if coil is really hot, they can fail with an open connection inside. Condensers fail, more often with the newer replacements. Also wiring can fail, but usually not a "cool off and it's OK" thing.
- If you have spark and it starts after sitting, you may have a fuel flow issue, the float bowl runs dry and takes a while to fill again.
The thing to figure out is if the time it runs is random or it pretty much fails around the same time every time. The heat/cooling period may be a red herring, but has been pretty consistent in my experience. I had an engine that would run about 5 minutes, then wouldn't restart , turned out to be the exhaust valve stem had zero clearance to the tappet, once it got hot, the valve couldn't close.
Keep us posted, we're here (randomly) to help..