Outdoor Power Equipment and Small Engines - John Deere 170 mower won't start when warm

I have a JD model 170 lawn tractor,18 years old, with a 14 hp Kawasaki engine. It starts and runs fine, but after turning it off, will not start again for several hours. It turns over, just won't start. After several hours, or next day, it starts again and runs fine until I shut it off. I've tried restarting after removing gas cap, no help. Possible culprits?
Thanks!

Is there spark?? Is the plug wet after trying to start it?? Is this a magneto or a battery type ignition??? Check a couple of things & let us know.... Roger

Sorry about that.
It is a battery, electric start tractor. I am getting spark, not sure how strong though, - that is beyond my limited expertise. I also replaced the plug.
Thanks again.

Could be valve clearances.
Does the engine seem to spin faster or easier when it will not restart?

I was also thinking valve clearances or possibly the igniter. Does it spit and pop when trying to start sometimes?

What is the model number of the engine?

Do not be concerned about strength of spark. Do you have spark during the period of time it will not start?

If you have spark and it will not start, squirt a little gasoline in the carburetor. If it starts you have a fuel delivery problem, fuel pump maybe. If it does not fire off and/or start I suggest you adjust the valves. With model number I can give you the specifications.

Install new spark plug.

18yr old 14hp kawa on a 170 I figured it a FC420...

I agree though, check for spark (any when it will not run) and fuel delivery.

I pulled the plug after failure to start, and is dry, so looks like at a minimum a fuel problem. I'll pursue that. Thanks all for the great suggestions, much appreciated!