We had a 45hp Wisconsin V4 on a small self propelled Ag sprayer back in the day. It would never like to start when the engine was hot. We fought it, and never really figured out why. Now years later when it doesn't matter, I think I now know the solution.
The issue was, as Turbinator has found, boiling gasoline in the fuel bowl in the carb..
I remember how lots of heat would radiate back up around the intake, and it would take 20 minutes before you even bothered to try and restart the engine. Of course the engine was some what under powered for the task it had, and it was used in 80+ degree weather. We used it for several years and sold it to a neighbor who used it years more. The engine was still the original when the neighbor sold it. Their advertising claimed long life, and they give that..
Regards, Kirk