Robert, have you checked the oil level? If over full, does it smell like gasoline? Does it have the correct dipstick? Does it have the rubber seal in the breather that looks like a piece of rubber hose?
Just questions that might give you a clue. If you have run the tractor for a long time and just now have the problem, it would seem like too much oil in the crankcase. If it is new to you, and you just changed the oil, maybe something like a wrong dipstick.
Interesting problem. Keep us posted to how you solve it.
tommyhawk