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super mta wants to diesel

My SM does that too , especially after working it. I let it idle to cool off some and then shut it off in 5th with clutch in and brakes held , and ease clutch out to stop the dieseling. Seems to be a common thing with higher compression Ms, and to me doesnt mean anything is actually "wrong". However, if your idle speed is set too high it will make it more likely to diesel. Mine has been doing that for 45+ years,lol.
 
Compression has nothing to do with it. We've got a 400 with compression out the wazoo. When you turn the key off it stops within 1/2 a revolution, whether it was just started or if it's been rode hard all day.

The problem is you've got a chunk of carbon in the top of at least one cylinder, which is glowing red-hot when you shut off the engine. That takes the place of the spark plug and keeps the engine running until it cools down.
 
Hmm, Well thats one stubborn piece of carbon on mine then ! lol Plowing and discing ,grinding feed , ect. hasnt broken it loose in 45 years ! Never had an H or C diesel on me....
 
Compression does have something to do with it as combustion temperatures are higher. It is something in the combustion chamber that is hot enough to ignite the incoming fuel charge. Usually carbon, may be edge of head gasket, spark plug thread or tip. If it does it when not even working it hard, you may have too hot a spark plug. Set idle speed as slow as engine will run decent, let it cool down, and if that don't work, kill it as I never like to hear a gas engine run on after shut off. That is the reason different mfgs used so many different methods of controlling this. That is one thing I thought Moline did right. They had a spring loaded low idle stop and to shut down you pushed throttle farther and it fully closed throttle plate.
 
With out seeing what ya got as for pistons and not knowing what the ing. timing is set at or if the centrifugal advance is sticking or not and like Pete said plug heat range and one other small little thing here your gas . If the timing is set tofar advance or to retarded to far and low octane fuel and idle set to high will cause this. So first check what plugs ya got in it ya do not want HOT plugs like D21's or D18's I have the best results from either 3116 or 386 Autolites or C86 A/C's Next check timing and see where it is at and do this at full throttle and set for 27-29 degrees.Check engine idle and set low idle at 450 -475 . While ya got the plugs out look in the hole and see how far up the piston comes , If the dome stops half way up in the spark plug how ya got normal domed pistons IF that dome goes way on put ya have the hight alt. pistons and here your going to need to up the octane rating of the gas ya burn . Check the cent. advance and make sure that it is working and not sticking in retard .
 
In automotive too they used to have all kinds of little devices to control dieseling , most were designed to close the throttle tighter at shut-down or stop fuel flow via a soleniod. Fuel injection cured it completely.
 
I am sure it is possible for almost any motor, but a SM seems to be more suseptable to it for what I have seen in my machine and various farmers I know who have them. Same is true in cars, some engines were more prone to it. My SC has personally never done it, even when worked pretty hard . Is your idle speed set too high maybe ? Like you, I always allow them to cool awhile before shutting down. My SHs have never dieseled on me either, even after working the snot outta it,and if you have ever had an H on a grinder/mixer with cob corn or oats you will know what I am talking about ! lol
 
We had an M with a 264 in it and rebuilt it up to a 281. This tractor would do the same thing. When it was rebuilt everything was rebuilt( Fire Crater pistons&sleves,bearings,Carb,dist and head) It was rechecked several times and everything was perfect. When we shut it down we would shut off fuel or put it in fifth gear and let the clutch out just as it was about to stop.
 
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