It doesn't matter if the coil seems to be ok when you check it for spark, it's what happens to that coil after it gets hot. Since it seems that you have covered all the other bases, try installing another coil onto this engine. My guess is that your problem will go away just as soon as you replace the coil with a new one.

When it runs for 5-15 minutes, does it run well?
By "crank", we mean the engine will spin over from the starter motor. Is that what you mean?
"Fire" but not run means there is, at least, occasional combustion occurring in the cylinders.
We need to make sure we're on the same page with terminology-
What was the appearance of the old spark plugs?
BTW- There NO need for "premium" fuel.

Yes, it runs very well for as long as it will run. The engine spins fine (no problem with the battery power or starter). If there were "fire" while the enging is trying to crank then pouring gas directly into the carb should at least get a pop or backfire or something. The old spark plugs were dark but not fouled. Replacing them was a low cost shot in the dark. So was the premium fuel.

"After engine cuts off it will not crank again until it's cool.
It appears to have fire all of the time but will not crank even if you pour gas directly into the carb."

"If there were "fire" while the enging is trying to crank then pouring gas directly into the carb should at least get a pop or backfire or something"

I'd agree that if you have a GOOD spark, you should get something by priming the carb, UNLESS the engine quit because it flooded out.
When it quits are you getting a lot of black smoke?
If so, I would clean the needle/seat on the carb.

If not, I say the ignition is failing.
If you still have one of your old spark plugs, open up the gap to about 3/16" and use that for a spark tester immediately when the engine quits.
A weak coil COULD provide enough spark when there is no pressure on the plug, but fail under compression.
I'd also look for a bad connection on any primary ignition wiring. maybe a contact/terminal is a bit "flaky" and heat causes it to it to move just enough...? (probably unlikely, but??)

Popular opinion is the ignition coil so I have ordered one. Should have it in about 2 days and we'll see if that is the problem.

Well, afetr you replace the coil ,if it runs fine disregard my post ,if not, check for a wire that is chafed and grounding out your ignition .....I have seen this in the past where as the motor warms,and vibration changes the wire will hit metal creating a ground from the coil killing the spark,then when the engine cools the wire no longer makes contact and it starts all over again....also vibration at different frequecies (sp) will vibrate a wire to ground and again kill the engine ....it's a shot in the dark but worth looking into.Good Luck Jim

You ordered 1 coil? Post your engine's model numbers so we
know what you have. You might have an engine with smartspark, and that would change things a bit.
We need model and spec numbers.

Fish

If the coil doesnt fix it, I think you have problems with sticky valves or improper valve clearance which manifests itself when the engine gets hot. Easiest first try for sticky valves: Put marvel mystery oil in the fuel and go for a drive. More difficulcult if that doesnt do it is check valve clearances. I think they are being held open when hot prohititing compression and startiung

Richard Debertin
(DavidLD's older Brother)
David would recommend some Seafoam mixed in the gas along with the marvel mystery oil.

Fish, My tech says that the actual part name is an ignition module, not a coil. I should have an answer on whether it fixes the problem today. The engine is about 15 yrs old so I don't know about the smartspark thing. I don't have the model numbers with me but I can get them tonight.
Richard, how much marvel should I put in a 3 gal tank full of gas? What is Seafoam?

Do not waste time with the miracle crap, there is no adjusting valve lash on a Kohler Command, they have hydraulic lifters. The Spark Advance Module, or Smartspark
could be the problem, but I doubt it. Otherwise, your engine has two ignition modules [coils]. More than likely,
you will find you have a corroded terminal somewhere, like the keyswitch, that is giving intermittant, or weak
voltage to the SAM, or spark advance module, giving you a
wide array of symptoms. If your tech wants to, have him e-mail me direct at Fisher40037@peoplepc.com, and maybe we
can resolve this and save you some money. I will make a guess, is this on a Craftsman?

Fish

Not a Craftsman, but probably the same mower in effect. It is a Yard Pro made by CYP (Carolina Yard Products). The coil that I ordered has the plug wires built into it. It is being installed as we speak. It wasn't terribly expensive but it will be if that does not fix the problem. Stand by.

I had a tractor with a 16hp Kohler Magnum engine. It was fine when it was running, but it wouldn't start hot. Everything seemed to be in order ... spark/fuel. The dealer wanted to do a valve job, rebuild the motor and whatever else. He said the compressions were low and unequal on the cylinders and got worse as it warmed up. Right! Plus, he couldn't duplicate the problem. The first time I ran it, after getting it back, it did the same thing.

I changed the ignition module/coil and never had another problem. It has been sold to a friend and is still mowing grass.

My point is, the Command has 2 "coils" or "modules, one for
each cylinder. The liklihood that both of them "go out"
at the same time is not very high, as the engine will run
on 1 cylinder. A wiring problem grounding out both coils
is possible, if it has a sam module, that would be the the
most likely trouble spot.
The ignition coil has but 1 spark plug wire, and no other wires on it, just spade terminals. If you have
a different looking ignition coil, then you do not have a Kohler Command.
Fish

I meant to say American Yard Products not CYP. The engine is a Kohler Command MV20. It is a single ignition module with two spark plug cables attached. My tech installed it and says the mower is running like new. Many thanks to all who responded to my question. Without so many concurring opinions I would have been reluctant to invest in the coil/ignition module. Thanks again!!

An MV20 is a Magnum, not a Command! Totally different engines!
Kind of makes troubleshooting a moot point.

Now that is some funny ####

Those pesky MV20 Commands..........................................

I wonder if he even read my last post......................

Bill, we do not get paid enough for this..............

Fish

CV20=Command Vertical 20 HP
MV20=Magnum Vertical 20 HP

Now if you would have took the old coil, and holding it by the spark plug wires, dipped it into a cup of Marvel Mystery Oil, that would have fixed it too......

But now, since the mower is fixed, and the problem was
the coil, on the MAGNUM,....

Did he check for voltage on the kill wire circuit, which would have damaged the old coil, and WILL damage the
new one?

That is the $100 question.

Coils do go out, but many times, if not most, they are
damaged by stray voltage that gets into the kill wire
circuit. Partial voltage damage, then the coil comes and
goes out when hot. Full 12 volts, it goes real quick.....

That is the question now.......

Fish

Apologies with thanks again to all. Engine is a Magnum.

What about the stray voltage possibility?

Fish

I take paypal.................. my new suffix for my
signature here....................

What about the stray voltage possibility?

Fish

I take paypal.................. my new suffix for my
signature here....................

Broken Flywheel