M fouling spark plug

Bryan Carroll · Mar 6, 2015

I have a M Farmall that keeps fouling the spark plug on #3 cylinder. When i take the plug out it is dry & brownish gray looking. When i replace it tractor will run good for about 20 min. then foul again. A neighbor said it could be a burnt valve causing the problem. What do you guys think? PS there is no oil on the plug whatsoever.

Janicholson · Mar 6, 2015

Three Ideas. Measure/Change plug wires to see if it is in the wire. (an Ohm meter should read at or near zero ohms on a solid core , or Magnetic suppression wire. Carbon resistance wires are not recommended)
Change a different plug from a different cylinder into that hole and see if the misfire follows the plug.
It could also be a vacuum leak allowing that cylinder to get a lean mixture from the intake manifold. Gaskets and cracks are possible, some crack internally into the exhaust manifold. Jim

El Toro · Mar 6, 2015

Try opening the main jet adjusting screw to see if that helps. Hal

rustred · Mar 6, 2015

(quoted from post at 16:47:21 03/06/15) I have a M Farmall that keeps fouling the spark plug on #3 cylinder. When i take the plug out it is dry & brownish gray looking. When i replace it tractor will run good for about 20 min. then foul again. A neighbor said it could be a burnt valve causing the problem. What do you guys think? PS there is no oil on the plug whatsoever.

well , check your compression on the engine then tell us and then you will get an an answer. anytime a plug problem persists , compression check is the first on the list. does not have to actually be a burnt valve but a low cyl. as 50-60 lbs. will miss fire and foul them .

M fouling spark plug

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Bryan Carroll

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