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Farmall M wont shut off

A

Anonymous-0

Well-known Member
My 1948 Farmall M wont shut off most the time when I try to shut it off. It will start to sound like it is going to, but then it just barely keeps turning over. I will then give it full throttle, and smoke comes out of the air cleaner, and it will then usually shut off. It is a 12v. system with alt. Can anybody help me here? I want to take it on a tractor ride saturday.
 
could the timing be off? how about the 12 v conversion do you have a resistor , diode or the little lite? or is your alternator a one wire job ? im just wondering out loud
 
That's called dieseling, after-run or run-on.

It's caused by a hot engine and way too much throttle opening. Slow your idle down and have the hand throttle at the extreme slow position.

If the hot iron doesn't get the fuel, it can't continue to diesel.

Allan
 
allan gets the cigar,also will add that it likes to take place in an engine that has some carbon build up, the carbon is hot and ignites the fuel.
 

I had the same problem with mine !

The timing was set correct , it had 110 octain fuel in it and everything was new and tuned on the dyno.

It turned out that inside the voltage regulator there is two sets of contact points that the correct gap must be set.

After prying all the tabs open on the brand new "American made" one that the one set of points was loose and open to far. The correct gap is .020.

After setting the gap it shuts off perfect every time.

We chased this problem for a while, it does have something to do with feed back. If i tried to turn it off at 900rpm or more it wouldn"t shut off, but if you ideled it down as loww as possible it would.

It did this on a hot or cold motor.

I went as far as buying a brand new wireing harness and having the generator rebuilt.
 
Common problem, pull the choke lever out when you turn off the ignition. No air, no fire.
 
Tn Terry is right on the money. Install one ohm light or diode in-line, along with a small switch. When you shut off your ignition switch, then switch your diode switch. The engine will stop. When you get ready to restart, switch the diode switch back as well as your ignition switch and you're back in business. Note: Until you get used to this, keep an eye on your ammeter. One way you switch the diode the battery charges quite a bit, the other, much less. You will get used to it.
 
a diode is a one way switch only letting the current travel only one way.thus preventing feedback when the tractor is shut off. so whats the extra switch for?
 
Meanwhile, throttle her back, put her in a high gear, step on both brakes, let out clutch and she will shut down. I have one that has not switch at all!
Wayne
 
That's called dieseling caused by carbon build up in the cylinders or timing being off. If its carbon theres a few ways to fix. #1 is to add a qt of ATF to 5 gal of gas and run it. #2 is to pull the air intake tube off and when its running spray a water mist into the carb. But of course it would help if you can explain it better because any one of use could have the answer because you do not explain things well
Hobby farm
 
I agree, a diode is needed to keep the juice from back feeding to the coil. Pulling the choke will work yes, but without any spark you will not need to choke it. Some how the ignition is getting shut off. If it does not have a diode in line it needs one. Good Luck
 
Allan in NE is on to it!!!!
Set the Idle down so it goes pretty darn slow with the throttle closed. (if it had a mag it would need to be just above the trip point of the impulse)
But without, it can be set very low. Then just apply the brakes and let out the clutch in high gear as you turn off the ignition. Gauranteeeeed.
JimN
 

That engine has to be carboned up REALLY BAD for it to "diesel" on indefinitely.

You also have to WORK the engine to get the carbon hot enough to ignite the fuel for "dieseling" to occurr.

If you're just firing up the tractor cold, and it's doing this, the alternator is backfeeding the coil and you need to add a diode.

At idle, the alternator isn't providing great voltage, which would explain any erratic running.
 

Well that just blows the diode theory right out of the water...

A diode is an electronic device that acts like a check valve, and only allows electricity to flow in one direction.

On a normal 3-wire alternator, you need to run an extra wire from the ignition switch to one of the terminals on the alternator to provide electricity to "excite" the alternator and make it start charging. This is the line that usually goes to the idiot light on your car's dashboard.

If you don't put a diode in this line, the generator will push electricty back through this line to the ignition switch. Since the coil and alternator excite wire are tied together on one terminal of the switch, the electricity goes straight from the alternator to the coil, and keeps the engine running.
 
Put a test light on the switch side of the coil and see if power is getting to it. If it is the switch is bad or something is backfeeding it. If no light, then it is carbon in cyls. If you have a mag, then unplug one spark plug wire and see if it is sparking, no sparking = carbon. If sparking, may be the shut off not working in mag.
 
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