I had a similar problem with my old ski boat (with a 1993 Indmar engine) and tried for a few years to figure out what it was. Took it to the dealer numerous times and they always found things to replace and charge me big $ and low and behold I would get out on the water and the same thing would happen again. Hard to replicate the conditions that caused the problem in the garage. Wouldn't start when it was hot.

After a bunch of research and trial and error I did 2 things that fixed it:

1. Thought it was a vapor lock issue with the fuel and I added a supplemental electric fuel pump back by the fuel tank. This would pump cool fuel through the vaporized fuel that the mechanical fuel pump on the motor could not do.
2. Replaced the coil and the coil ballast at the same time.

Not sure which one was causing it, maybe both were, but we never had a problem with warm/hot starts ever again and the boat fired right up even after long storage times every time we took it out which is something it rarely did before. It took a lot of cranking to get it to fire up when it had been sitting for a few weeks. Getting fuel to pull through the lines with a mechanical pump took a long time and the electric booster pump really fixed it.

Both were pretty simple and inexpensive to do - I have very basic mechanical knowledge/experience.

I did that about 6 years ago and never had another problem with it.

My guess is that one or both are causing your problems too.

Good luck
Craig