need help; engine running rough then cuts out

Mon Nov 14, 2005 10:13 pm

I'm trying to troubleshoot my Farmall Super C. The engine starts up fine with use of the choke, but if I put engine to full throttle, it cuts right out. If I leave the engine run at a lower throttle, it will run for a little while, but cuts out once the engine starts to heat up. I've changed the fuel, cleaned the carb and fuel bowl out, and checked the plugs/wires. Any suggestions with where to go to next or what could possibly be the culprit?


Mon Nov 14, 2005 11:40 pm

With the heat up only I might suspect the coil but with the full throttle part is it with the choke out or in? I would still suspect fuel problems and goo over it again. does the float move freely? Is there a screen on the in of the carb. I would remove the needle and blow everything out again. Keep the choke out as you increase the throttle. If that keeps it running it is fuel. As a further check hold a small jug of fuel in the air stream so that it will suck fuel. Does that keep it running.


Tue Nov 15, 2005 12:57 am

When checking out the fuel system. Check the manifold for cracks and the manifold gaskets - vaccum leak.

Weak spark???


Tue Nov 15, 2005 7:48 am

The description at startup indicates too much air or not enough fuel since it runs well with choke. The throttle-up condition sounds like fuel starvation but the kicker then is the fact that after warm-up it gets worse. It really sounds like air infiltration to me. Intake manifold gasket or crack in the manifold would be high on my list of suspicions. I think Eugene is right on.

Tue Nov 15, 2005 9:37 pm


There are a few holes in the exhaust manifold, but I had kinda ruled them out early on because they've been there since I got the tractor. I've tried to fill them with JB weld, not sure what else to try to do to fix the holes besides replace the whole exhaust manifold. I've got a carb rebuild kit on the way, hopefully that should do the trick. This problem just came on this year, and it was really all of a sudden when I was using the brush hog. When the PTO is engaged, the engine will cut out alot quicker than if I run the engine without the PTO engaged.


Tue Nov 15, 2005 9:52 pm

JB - the problem will be with the intake side of the manifold. Rough running is very much related to improper fuel mixture, cutting out means not enough fuel or too much air. Air infiltration (vacuum leak) can occur anywhere along the intake path - gasketed surfaces, loose manifold bolts etc.

Wed Nov 16, 2005 12:56 am

Cheap investigative tool. Try the propane trick on the manifold. Running tractor, unlit propane torch, pass gas jet along manifold and manifold gaskets. When the engine speeds up - problem area.

Rusted or burnt out manifold. No real good solution other than obtain a good manifold. Biggest problem with a manifold in poor condtion - repair one spot and before long another hole developes.


Fri Nov 18, 2005 12:17 pm

What happens that the engine speeds up with the propane tourch :?:

Fri Nov 18, 2005 12:34 pm

Phil, when the propane gas gets sucked into the area of air infiltration, the engine will speed up because there is more combustible fuel in the chamber. Instead of sucking in air and reducing the fuel / air ratio, you are adding fuel.

Fri Nov 18, 2005 12:36 pm

Don't forget that since a cub has a governor the speed up will be small or momentary, as the governor attempts to correct, where as a car without a governor will change drastically.