I've been working on this 1950 side mount (12V) trying to diagnose low power and run time issues. Oil pressure is 25PSI cold, 10-15 hot idle. I have double checked point gap 0.025 and firing order.Symptoms:
Tractor starts right up and when warmed up, idles very nicely. It throttles up well, and runs nicely at 2000-2100 RPM without a load on engine. But when throttling down, it won't return to idle, and will instead run at about 900-1100 RPM on the tack. In terms of power under load, the engine will die if you use the brake to make a turn with engine in the 1000 RPM range in 3rd gear. In 4th gear, it barely has enough power to get up a small incline, even at 3/4 throttle. If you use the throttle to give the engine more power when the engine is under a load, it will not respond with more power. If the clutch is pressed after trying to put a load on engine, the engine races and will begin to hunt. If you try to idle down at this point, engine will continue racing for several seconds before it begins to slow down. It will not return to idle, but will run in the 1000 RPM range again. Observations:
When engine fails to throttle down, I can push the throttle at the carb down to bring it back to an acceptable idle. It then idles very nicely. I've noticed that when using the throttle lever, the carb-to-governor arm seems to bind and will not return to the idle position, even if the throttle arm of the governor has returned to the idle position. Again, pushing the arm back returns engine to acceptable idle. I have checked and adjusted the linkage per the FO-4 manual. The governor spring also seems to fit snug without any up and down motion. There is nothing catching the carburetor linkage to cause it to bind. Removing the governor, this wear pattern was in the housing: 
I've never worked with a governor before, but the side to side motion of the governor shaft seemed pretty sloppy. The wear on this ball is consistent across all three.  Based on the wear patterns and the symptoms I've described, do you think I'm on the right track? If i am on the right track, is this wear significant enough that the governor should be completely replaced or should I invest in a rebuild kit? It's worth noting that I initially thought this was a carburetor issue. The carb on this tractor was professionally rebuilt a couple of years ago by a shop in VA that I've had good luck with. But to double check, my son and I rebuilt another carb last weekend that we had laying around. I have the same problems with both carburetors, which I believe rules out the carb. Thanks for your thoughts!
Colin, Stumped in MN
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