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Farmall 400 Running Rough

C

chrisfarmallf20

New User
On very low idle, it seems to run quite smooth. When sitting but throttle opened-up...the motor runs extremely rough. When under load, however, it does even itself out a bit. I had the carb off and cleaned it up very well. No problems there. Getting fuel from the gas tank just fine as well. Any help or ideas would be great. Thanks.
 
Couple of thoughts - make sure ignition system is in good shape. My M runs like crap when the points and condenser need changing. You can also look for leaks in the intake manifold. If your tractor is running try pulling the choke part way. If it straightens out but starts to smoke it is probably an intake leak.
 
I will ad that a non functioning centrifugal advance will provide that roughness. Another thought is the distributor bushing. if worn, it allows radical timing variation, and misfire. Jim
 
One important question, did this just start happening, or was something, even seemingly insignificant, changed? Why was the carb off, to fix this problem, or another reason?

Agreed with what the others have said - but I do think it's important that it runs smoother under load.

That generally means the governor is opening your carb further to keep the same RPM level.

So, if opening the carb smooths the engnine out -at that same rpm level, it makes me think the problem is carb related.

Cleaning a carb thoroughly doesn't necessarily mean it's going to work perfectly.

I'd go through what others have said, and check/fix the easy stuff, especially the points, and checking the advance.

But I wouldn't cross the carb off the list as a known good.

I'm not familiar with the carbs on the 400, but I'm assuming there are some tolerances here or there worth checking on it.

If you come back to the carb, I'm sure others here could give you some pointers one what too look at.
 
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