Farmall M Carb Settings?

Faster346 · Oct 19, 2009

Is there any set presets for the three mixture screws on the Farmall M carb? My uncle was messing with my carb since the tractor had no power, and would die whenever you gave it throttle. He got it running decent, and it has power now, but it's running really rich. It huffs black smoke while it's idling, and under throttle, and when it's in the lower RPMs you can hear it loading up, and it almost sounds like the engine is missing. I was just wondering where the screws should be set at. I know they can be touchy. Thanks.

-Lance

old · Oct 19, 2009

It should only have 2 screws on it. The high one is the idle screw and you turn it in to make it richer but a start point on it is about 1.5 turns out from bottom. The lower one is the main jet and it should be around 4 or 5 turns out form bottom. The make it leaner you screw that main jet screw in a tad just till the black smoke stops and you should have it about right

rustred · Oct 19, 2009

that third top screw is for the idle throttle stop.set engine idle to approx.425 rpm with this screw. a good # is 3 turns out for the btm.main adjusting screw. middle idle adjusting screw is 1 turn out and your very close. i set them as this after o/h and dont really hardly need to readjust.if your out in field plowing or working hard then may need to open the main 1/2 turn.

rustyfarmall · Oct 19, 2009

Rich, factory initial setting on that bottom screw is 3 turns out and if the tractor does not run at that setting then something else is wrong. 5 turns out will take the needle clear out of the metering jet and then you will have an over-rich condition.

Faster346 · Oct 19, 2009

Thanks for the replies. I bought a carb rebuild kit today and it recommended the screw settings (they were pretty similar to what you guys had suggested) and it ran decent, but if you throttled it up too fast it would pop. My uncle played with the screws while I revved it and we seemed to have gotten it pretty smooth. Pulled the plugs out and they're as black and carboned as can be (probably from it running rich and smoking like a diesel last night when the carb was all screwed up) So I'm going to pick up a set of plugs, and put an in-line fuel filter on it when I get off work, and see if it runs any better.

mhmalcolm · Oct 19, 2009

Watch out about putting an in line filter in these gravity fuel systems. Most in line filters are meant to be used with a fuel pump, and some of them can actually cause a restriction. The screen in the sediment bowl and the screen in the inlet fitting in the carburetor are all the filtering you need.

Farmallhal · Oct 19, 2009

Take a look at your oil bath air cleaner and make sure the oil level isn't too high in the cup. I had that problem on my Super C and I experienced similar problems. The in-line filter I installed caused more problems then it cured mainly fuel wouldn't flow when the tank was down a few gallons as there wasn't enoung head presure in the fuel level. Good luck and hope it is a simple fix for you, Hal.

Faster346 · Oct 19, 2009

Really, I didn't think about that. I was on Antique Tractors Forum and several people there told me to run an inline filter, and that was what they have had good luck with.

I never thought about the oil in the air cleaner. I'll look into that in the morning. Thanks!

rustyfarmall · Oct 19, 2009

I know which forum you are talking about. I got booted off of that forum because I was giving straight foward and correct answers to questions. Several other registered members canceled their membership shortly after.

John M · Oct 20, 2009

Ah, I thought it was for other reasons. Ive always valued your advice here and there, although I havent always agreed with it. I just dont think Jr would have booted you for giving good advice. If I recall, something similar happened here a while back to someone else who wouldnt stop what he was doing even after being asked by the owner(s).

Farmall M Carb Settings?

Faster346

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old

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rustred

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rustyfarmall

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Faster346

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mhmalcolm

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Farmallhal

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Faster346

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rustyfarmall

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John M

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