" vapor lock" ......To me when you say this it means will not start and that usually happens after the engine is shut down . The fuel boils out of the line/carb and the engine is starved for fuel until it has be replace as a result of restarting the motor. Just trying to understand what you are trying to describe .
Next you say "cool down and it starts back up with no problem, runs like a scald rabbit"
"scald rabbit" ? driving it putting your foot in it, tri-power open ? that kind of scald rabbit ?
or are you saying it ideals smooth and is overall drivable ? if the later,
I would check the choke adjustment make sure it is open at operating temp.
How far of a cool down? cold ambient/room temp or just anywhere below 185 ..
I believe that tri-power would have progressive linkage, having trouble visualizing vacuum actuated outboard carbs.