Cub Cadet FAQ's
Engine Surging or Hunting
A LEAN fuel mixture will cause hunting. A loose throttle
shaft will most certainly cause excessive air leakage downstream of the fuel
supply causing a lean mixture. Closing the choke plate will correct the hunting
because it is enriching you mixture. Kohler has shaft kits that help you repair
One thing that you can do to test if it is the shaft of something else is to put some grease around the shaft and then run your engine. The grease will not last long, but will plug the air leak (if that is where your problem is) and cause the engine to stop hunting. This is one way that I use to diagnose the leaking throttle shaft problem. BTW, Kohlers and old Tecumseh carbs are fairly tolerant. The shaft is usually visually loose before you get the hunting. I have seen Mikuni carbs start to give problems with only minimal wear on the throttle shaft, however.
Another problem that I have seen (when the shaft is good), is a clogged idle fuel passage. I have learned the hard way to pull all welch plugs on old, badly fouled carbs and use a jet of solvent to clean the passages. One old Tecumseh carb (built by Walbro) even required me to clear the passage with a small drill (back end, not cutting end).