140 compression

The amount of compression for the lower 2 cylinders indicate some ring wear or minor valve seating problems. But overall, the pressures are more than enough for a good running engine. The only problem is that differences in compression can result in a "less smooth" running engine since the combustion pressures are not equal along the firing cycle and the "pulse" hitting the crankshaft through the rods will be somewhat lower for the 2 110 PSI cylinders. The differences you found are not major, but are worth looking into. I would try adding a few shots of oil to the weak cylinders--(one at a time) and then run the compression check. If the pressure goes up, then the rings are letting some pressure by them. If compression readings don't change, then valves or head gasket may be the culprit. Also, pay close attention to your oil condition--color smell, etc. Same for your coolant. Look for oil in coolant and milky oil--that could help isolate the problem, if it's anything beyond ring or valve wear. By the way, if you just got that tractor and it hasn't been running in awhile, you can try soaking all four cylinders in Marvel Oil--sometimes the rings can stick a little in the grooves and they need a little help getting back to their "sprung" shape and size.