tractor keeps running after its shut off

[Kurt LaGrander]

My 450 farmall keeps running after I shut the key off. Popping and snorting. Is it out of time or is it the carb?
 

[old]

Running as in what is called dieseling or running as in true engine running?? If dieseling that is caused by hot spots in the engine which in turn is burning the fuel that is still being sucked into the engine from the carb. It is caused by carbon build up in the cylinder on the valves and the top of the pistons. On some it helps to pour a qt if ATF into 3-5 gal of gas and run it that way to clean out the carbon
 

[DeltaRed]

My SM hasa done that for years,even right after it was o'hauled'.Timeing has been checked...Is this because it has too much cumpression?The head was 'planed',and it has hi-altitude stephead pistons.It's always been worked hard,so its never had a chance to get carboned up.Are there other things that could cause that?
 

[Kurt LaGrander]

Yes my 450 was just overhauled too. Not sure why it would be carboned up?
 

[old]

Again can be caused by hot spots as in shut down with out letting it idle for a bit to cool down some. Of course if you turn off the gas then let it die that way then turn off the switch that will stop it or should
 

[old]

No would not be from carbon but form hot spots caused by not letting it idle some to cool before shutting it off. Of course on way to stop the problem is shut off the gas let it die then turn off the ignition
 

[Owen Aaland]

Too high a heat range spark plug can also contribute to the problem.
 

[Kurt LaGrander]

What plug should I be running in a 450 farmall?
 

[gene bender]

Just shut it off in gear. You have bad plugs doesent hirt to cool the engine down a little before shuttiing off.
 

[CNKS]

You can also stop it by pulling out the choke, that's the way I stopped my M. Some say this dumps more gas in the cylinders and washes the oil off. Did that for years, but the M saw little use.
 

[mkirsch]

You've got a fresh engine with tons of compression, and you're working the tractor like a government mule. That creates excessive heat, and the hot spots old is talking about.

There is no one "right" plug. You need hotter plugs if you just putter around the yard, and cooler plugs if you flog the thing.

In Champion plugs, the higher the number the hotter the plug IIRC. D21 is hottest, D15Y is coolest. Autolite is not as straightforward with their numbering so I don't want to stick my neck out on that one. People don't like Champion plugs anymore though.
 

[teddy52food]

Not out of time. When you turn it off the spark is gone. Idel it down for a while to cool off then ride the clutch in high gear as you turn it off.
 

[the tractor vet]

Ing. timing not set correctly , wrong heat range spark plugs, fuel screw not set correctly . idling to high , to low octane fuel . centrifugal advance not working properly (leads back to ing. timing) , running way to hot ( that goes back to lean fuel mixture , timing , wrong heat range of spark plugs , sticking thermostat, poor coolant flow dirty rad.)
 

[Berth 29 opinions]

When we had a tractor that developed this problem, (AC D15) we just turned off the ignition with it in gear, let the momentum take it to a stop. In the barn hanging tobacco we would get in place and let the clutch out when we shut it down.

The 140 at one time developed a backfeed thru the alternator, turned it off, the engine would restart. With the key off, 6-8 volts was backfeeding to the coil. unplugging the white connector on the alternator solved this before turning the switch off.

What it would do is cut off, and before the engine stopped turning the current from the alt would fire a spark plug, which would turn the alt, firing more spark plugs.
We figured it was getting the 6 volts from somewhere, removing the neg battery cable had no effect, unplugging the alt did.

 

[rustred]

the best cure for run-on is to adjust the idle screw so engine actually stops when throttle is at slowest idle position. this puts the throttle plate in the fully closed position and it can not run.might not get tractor to completly stop with the screw backed right out though, but it sure helps the problem if yu can get the idle slowed right down.
GM cured this problem with an electric solenoid so that when key is turned of the solenoid is deactivated and closes throttle plates completely.