Farmall Cub

when I set the throttle the engine rpm stays set for a minute or so then speeds up, sounds like a governer problem to me, any other things could cause this?

Straylight.

Sounds like it could be a dirty / sticking governor. How does it run after you get the rpm's up?

Couple more things to check, make sure linkage goin to throttle isn't dragging on engine block, and also that were the shaft that goes across the front of the engine isn't loose in the coupling at the governor. It shouldn't move easily.

Good point John. I had one of mine where the linkage was dragging on the intake pipe from the air cleaner. Acted just the same way. Re-positioned the tube and no more problem.

check the thrust bearing