you Might try building a heat shield to isolate the carb from the intake/exhaust manifolds.
Sandwich between the carb and intake.
This type can be made from sheet aluminum.
Just an example made for a Holley but easy to make.
https://www.holley.com/products/fuel...s/parts/108-70
Your timing can effect engine heat which causes vapour lock.
Do you have lots of initial timing?