Farmall C runs rough under load

My 1947 Farmall C starts and idels OK, however when I do something that requires more power (hauling a trailor, pulling a stump, etc) it often starts runing very rough, making kind of a "vroom, vroom, vroom" sound, the engine speeding up then slowing down, etc. I have to get off the tractor and manually stabilize a bar that runs from the carb to the governor. Is this a carb or governor issue? Any help is appreciated.

I have a C that does that with no load. Bought at auction, have not had time to look into it. I suspect the governor.

My take on it is that the Governor may have issues. If the governor rod (that you held to quiet the "lope") is looked at while it is loping, looseness might be observed. The first place to look is the condition of the linkage from the lever (near the front of the engine left side) to the carb, that rod. With the engine off do the following: Move the hand lever at the driver's station to its wide open position. Go to the linkage at the carb on the engine side. Wiggle this rod forward and backward, not side to side. It should feel tight. now move the speed lever to almost idle. wiggle the linkage again. If it is loose, and has free play, the link pins/pivots are worn, and possible the holes in the carb lever and governor lever. Make these pivot points have better closer fit. A fatter rod, welding up the rod end and reshaping, or putting bushings on the linkage is usually needed. This takes out the looseness that can cause this "Loping". If this does not help, or if the linkage is tight in its pivots, the issue may be in sticky governor internal pivot points, wear on those pivots, or a bad governor main bearing. The governor is difficult to remove without removing the radiator. (some say it can be done), I have doubts. If all else fails, it could be the carb, it may have a restriction in the high speed circuit. The load applied slows the engine, the governor correctly gives it more fuel and air to keep the speed steady.
The engine over reacts to this and surges.

Best of luck. Jim

Thanks Jim I will try your recommendations!!

I had a B that did that and it ended up being the thrust bearing on the front of the governor shaft. I found it the hard way after it dropped the ball bearings out of the cage and ruined two of the timing gears. But first check the easy and cheap things!

There is an adjustment screw on the bottom of the gov housing. Take it out & there is a spring in there. If the spring is all corroded replace it. If not adjust it in a little tighter.

The spring in the surge bumper mite be shot and could have bad bearings in the gov and the spring mite be on wrong. The gov housing can be removed to rebuild i just did one the otherday then make sure the linkage it set proper all the little thingscan add up. First i would try and give the surge bumper a little adjustment. The spring in the surge bumper screw can be replaced without removing the gov just unscrew out of its mount on the bottom

I'm going to key in on your statement "it often starts runing very rough" and maybe take a different slant on your problem. Does your engine really run rough or is it simply surging? If it is rough, you need to make sure the fuel and ignition systems are in order before you get into the governor. Maybe you need a tune-up. If the ignition is in shape and the caruretor is delivering enough fuel, the next thing to check is the linkage between the governor and the carb.

With the engine off, unpin the forward end of the rod that connects the governor arm to the carburetor. Push the control lever forward. Pull the (now disconnected) rod back so the carb is wide open. The pin in the linkage should be able to slide back in without moving the other parts. If it doesn't, turn the yoke on the front end of the rod to the longest adjustment that will let the pin slide in. Make sure that link moves freely with no binding.

Only AFTER doing all this, remove, clean and adjust the bumper spring as already mentioned.

sounds like govenor problems to me

Thanks everyone for all the great suggestions. I hope to try some things later this week. My other tractor (Farmall M) narrowly escaped major damage last week... our property was pretty badly hit by the tornados in western MA. We have about 100 trees down and will need the M to help clear the mess.