[sick472]

Overheated starters seem to crank less than desired when compared to cold starts, and bad wire connections when overheated will transfer less electrical power.

Slightly off ignition timing can also effect the crank rate of a motor that is up to temp. Don't ask me to explain that one, but I have found that a cold motor that starts fine with the timing a little off will have a harder time starting once it's warmed up.

Make sure all your wiring connections to the starter and battery are clean and shiny as mentioned, then look into shielding the heat from the system, and/or have your starter checked out. You should check your timing too, maybe retard it a bit when up to temp and try the starter right away.