Vapor lock is a starving of fuel at the carb bowl while a low
pressure-high temperature area in the fuel delivery system delivers
enough vapor that the fuel pump can't get to liquid fuel. You just
don't have that situation in a gravity system.

What you may be considering vapor lock in a gravity system may be fuel
boiling in the carb bowl due to radiated heat from the exhaust system.
This causes the float to sink in the "foam fuel". The bowl then
overfills, and the excess fuel is vented from the bowl into the air
intake, flooding the engine.

The key is that all aircraft carbs vent the bowl to the air intake,
allowing a way to flood the engine. This is not very well publicized.

TriPacers probably flood the second way. Cherokees could go either
way.

Does this jibe with any observations? Comments?