I had and old Tecumseh on my JD, from 1979. It had a mechanical governor inside the crank case. If that is the problem, you will have to tear it all the way down. The parts for the old Tecumseh's are getting harder to find. I personally think the best place for them is the scrap pile. That's where mine went and I crossed over to Briggs. On the bright side, maybe the arm on the governor shaft came loose and you should be able to get it set again. I have written down how to do that, I just need to find it again. Let me know if that would help.