See if you have spark when this happens. If not, then you could have a coil that stops working after it "heat soaks".

Explain what you mean by "will not start again".

Explaining exactly what's going on will help to eliminate a bunch of guessing.

If you have had used this tractor for a long time, as you say, it could be that when the engine heats up you are losing compression. Somewhere, a long time ago I remember reading that can happen I think it had to do with automobile engines. Still, the same principals might apply. I don't remember if it was caused by worn piston rings or valves. Maybe another forum member could explain if that could happen. Also, it could be an electrical problem. You could check this by opening the hood and letting it run in the dark. Just watch for sparks after it gets hot.

Good luck, and remember the number one rule in do-it-yourself mechanical problem solving : "Always check the cheapest things first."

I had a similar problem with a Kohler Magnum MV16. It seemed like everything was there .. fuel, spark, etc. It turned out to be the electronic ignition coil module. Dealer didn't have a clue!

I don't think it's a coil problem because a coil is one of those things that when it gets hot it'll cut out and not be consistant either with not starting cold or hot, so if the motor was working fine up until shutting off, then it isn't the coil. I think it's the fuel pump. Try this test when hot:
Remove the air filter and take just a little fuel and pour it down the carburator to prime it and if it starts up then you'll know it's the fuel pump. Just make sure also that there's no other problems left unchecked, like any loose fitting vaccuum hoses that need replaced,tight carb screws,intake bolts tight,no missing vaccuum caps, etc. Yes, there's a lot to check out with a problem motor, but that's where you get to know your machine---hands on. This is also where you may need a carburator rebuild, but with what you gave for a problem, it's hard to diagnose.

I disagree with troller_mo.

I've seen several coils, which would work fine cold, but quit when they were warm.

You could cool the coil assembly with some electronic component coolant, available in electronic stores, ... the problem being, to get in to it, to be able to spray it while it's warm.

On one car, I was able to duplicate the problem by warming the coil with a hair dryer.

I thought that also Tmajor, but a coil will break down during running and create a misfiring condition and progressivly get worse as time goes along and the engine getting hotter, and Garden_fool said that it wouldn't restart AFTER shutting down, NOT while cold starting or running conditions, so there's something else not letting the mower restart once it's hot. True there's not much electronics with these mowers, so I would check with other cheaper remedies before going to the higher dollar items and in the end, it may just be the coil, but with what was described, it just didn't sound like a coil.

It could be the coil - which normally stays a bit cooler than when you shut off the engine, and the cooling fan stops blowing air around everywhere... it's also possible that it's a bad spark-plug. It's also possible that it's a fuel delivery problem.

Pour an ounce of gas down the throat (carb) next time it happens - to eliminate the fuel problem.

Alternatively, pull the boot off the spark plug and see if you are getting a spark....

I'm new to lawn tractors but engines are pretty much engines. I didn't want to be giving advice in my first post but my first inclination would be vapor lock.

If there isn't any insulation between the carb and intake manifold, such as a missing shield or spacer, or the insulation has broken down, the heat of the engine can heat the carb float bowl to the point of vaporising the fuel in the bowl.

That said, it COULD be a coil as an intermittent coil, one with a break in a winding, can open circuit when it gets hot and expands. When the coil cools and contracts the broken winding's ends can close the circuit and it works again. If it were a coil I would expect the engine to stop running when hot though. That's why I'm sticking with vapor lock.

Cheers,
Hydrogoat

I meant to add that in a vapor lock scenario, while the engine is running, the fresh fuel coming into the bowl cools it enough to keep the fuel liquid. Once the engine is stopped and gravity or a pump stops feeding fuel, if the carb is hot enough, the fuel evaporates in the bowl.

Also, I would not pour raw gas into a hot engine's carb throat. Gasoline has an extremely low flash point and could ignite.

Sorry for the two posts, I'm not familiar with the preview and edit features of this site.

Hydrogoat

As I recall, in my process to lead me to the coil replacement, I took and recorded a resistance measurement from the plug wires to ground, when cold. After shutting the hot engine off, I reattached the OHM meter to the leads and watched it for a period of time. The resistance changed from the recorded reading. It may have even been different immediately. ??

I'm not familar with that kolher engine, But, here what I would check if the engine cranks over fast enough to start. First I would see as suggested if it getting fire to the plug or plugs when it won't start. Next I would use carb. cleaner down the carb. venturi if it's getting fire and if it cranks over fast enough to start (carb. cleaner is way more safer than gas IMO and you get a side benifit it cleans the carb some)(IMO dumping raw gas down a side mounted carb a fire hazzard especially right over a hot muffler not to mention a back fire).

I would also check the cooling air venting under the cowling and I would also remove the cooling shrouds around the engine and check the cooling fins on the block. With everything clean and getting proper cooling air you should be able to determine if it is a spark problem or fuel delivery problem.

still the same problem I would remove the head or heads and see what's going on inside the combustion chamber. I would look for carbon build up, burnt valves and piston slap.

Are you starting it with the choke on when it's hot? Try full throttle, no choke. That works with my GT225, which I believe has the same engine.

Your valve(s) might be sticking open. Check compression when it happens. Does it spin easy after it quits and you try to start it?

Thanks for all of the suggestions and ideas. I will start experimenting to find the problem. The last post from dave mn got me to thinking It seems like it does turns over faster when this situations occurs. I have also noticed that sometime when I cut it off it backfires. Could this be an indication that a valve is stuck open? And if so are there any solutions besides tearing into the engine? Thanks for all the help

I think you could just take the head off, remove the valves and decarbonize the valve stems (wire brush). I had a Kohler 12 HP that this happened to. I traded it before I fixed it (the dealer diagnosed the problem, I didnt try to cheat them).