fuel shutoff solenoid on M to control after-run?

zooeyhall

Member
I have a gas Farmall M I use to farm 160 acres. When I shut off the tractor I frequently get "dieseling" or "after-run". The only way I can stop it is by putting it in gear and letting out the clutch. Since this makes the tractor jump and/or move ahead, it's kinda dangerous.

I would like to install one of the IH fuel shutoff solenoids like are used on the Farmall 656 series gas tractors. And replace the current main fuel adjusting screw and packing nut. Wire it into the ignition switch system. I am told that the main jet is designed to give the proper amount of fuel, and the adjusting screw really isn't needed on these carburetors.

Advice? Opinions?
 
Do you idle it down and let it idle a few minutes before you shut it off?? I'd try this in case it has carbon build up and hot spots due to that. Put a qt of ATF in say 5 gal of gas and see if that helps
 
What is the idle speed? If it is idling around 5-600 rpm,slow it down to around 400 rpm.Since you are running premium,at operating temp,advance the timing until it just starts to Ping,or knock on a hard pull,then back it off a little at a time until the ping goes away.
 
make sure idle speed is at or very near specs. and throttle is fully closed when shutting off after giving cool down time. 2nd hint is shift to 5th gear and hold brake shut off and let out clutch, by using high gear maximum load will be on engine when clutch is let out and will stop engine without tending to move tractor as much
 
Why do you use premium? I use regular 10% ethanol in my M's and they will diesel if they are hot. If you set the brake hard and slip the clutch just as the engine is about to die the tractor won't jump. Mine run backwards sometimes instead of dieseling forward and I don't like that so I use the clutch. Pulling the choke will also kill them.

I use the main fuel adjusting screw. For heavy loads I need to open the screw until just before there is black smoke in the exhaust otherwise the tractor won't pull the load. I have to do this when pulling the NH Bale Wagon on the road. Then for lighter work it needs to be screwed back in. I think it is right out of the Operator's Manual.
 
Well to stop this on a M lets start with getting the ing.timing set like it SHOULD BE , Not where you think it should be . Next install the correct spark plugs . Check your dist for a stuck centrifugal advance of broken springs . Get you carb adjusted correctly and adjust the idle to what it should be BY A TACH not by ear. and last but not least let it set at idle for a little bit to cool down . Now IF and again i say IF you have high compression pistons in it and changed the head to a 4540 head and it has been milled down a bunch then you may have to step up on your grade of gas your running .
 
On a old M if it has never had the dist reworked then it could be running 40 degree advance at WOT . And your working with a TRACTOR not a small block Chebby SOOOoooo your advice is dead wrong , ya want a TRACTOR to PULL then you need to back off the timing and a old M will pull better at around 25-27 degrees advance a WOT.
 
But dont forget that carbon hold heat a lot longer than metal does, so your carbon on the domed piston is your temporary spark plug.
 
Ignition, timing or anything electrical have absolutely NOTHING to due with run-on. After the switch is off, there is no timing. Zero.

Pull the idle down.

Allan
 
It should have the 40 degree set up in it stock, I backed mine down to 22 degrees when I turbo'd it. It wouldn't hurt if he let it idle for a minute or so...best bet is to shut off fuel and wait till it runs out.
 
There isn't a stock M in the country anymore. Original spark advance was 40 degree with cast iron pistons. With aluminum pistons and overbore kit you have same compression ratio as a Super M which came with a 30 degree advance. If you have domed pistons, gas head, or fire crater pistons you have higher than stock super m comp ratio and need to back off the total advance. Over advanced timing creates hotter than normal spark plug tips, carbon deposits and contributes to dieseling. Sure the ignition is shut down so no spark but timing has everything to do with hot spots. Normally, if you have the idle speed down where it belongs and let it idle a bit before shut down they will conk right out. Total advance can be modified by filling the limiting slot in the distributor shaft. Trial and error but can be done.
 
If it wants to keep running it means you have some hot internal parts, it needs to idle awhile to cool down. We have the same problem with our C and I add a quart of diesel to every 5 gallons of gas. (regular with ethanol) The diesel lowers the octane and just seems to make it run better, and might reduce corrosion in the tank.
 
If the ing. timing is tofar advanced the combustion chamber temp will be higher and the plugs will act like a glow plug. Learned that many years ago .
 
I am with Tractor Vet. Fix the source of the run-on. Make sure the timing is correct set to PREVENT over-heating in the cylinders. Get rid of the carbon. Get the correct heat range spark plugs installed.

Lastly, make sure it is not running too rich, which could be part of the carbon problem.

Fix the source of the problem, don't circumvent it.
 
Why are you throwing your money away using premium fuel on an engine that has less than 6:1 compression? You gain absolutely nothing with it and have probably identified the source of your carbon issues.
 
I agree with the tractor vet and Tom Fleming on setting the timing where it should be along with insuring the other stuff too. Doing the timing by ear is asking for trouble.

I see no problem with you running premium fuel . While the engine does not need it, Premium seems to keep better in storage for me as it stores longer if tractor does not see lots of use.

Keys to setting the timing are using a tachometer to set the idle speed where it should be and then insuring the distributer is set for the proper advance for the pistons you have now.

I have pieced a procedure together from many of pete23's and Owen Aaland's posts in the archives that I used on both my Farmall h and farmall M to set the timing properly. I have put the formuals in there to boot for the mathematically challenged.

The great thing about an old m or an h is their simplicity. Adding an unneeded solenoid to them is pointless IMOP and otherwise ruining one of the old Farmalls true benefits in its simplicity.
 
I have a farmall m that I pull that has a little over 150 lbs. and I fixed that problem by turning the idle on the carb slower then motor will run then shut it off and push the throttle back works for me.

Robertw
 
"I am told that the main jet is designed to give the proper amount of fuel, and the adjusting screw really isn't needed on these carburetors." That applies to the SM, not the M, although it could have a SM carb on it. The SM screw is needed--5 turns out is for max power, it can be turned in some for lighter loads. It cannot be used as the one on the M to adjust the carb for smooth running. If the SM screw is turned in too far or adjusted like the M the SM will have little power.
 
set the idle down to 400 rpm! and you will be fine. basically that is the fix. you want the throttle plate darn near shut. as all the solenoid does is close it completely once switch is turned off.
 

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