In some engines a phenolic insulator is necessary between the carb and engine to keep the carb from heat soaking. When the carb gets too hot the fuel boils off and then when fresh fuel is drawn in by the pump it also boils building up pressure causing the pump to stop pulling fuel from the tank. Sometimes it's referred to as "Vapor Lock". I know my G26 did this with a custom made aluminum spacer block and I had to put the stock phenolic one back on.

Also, my MVVS 26 gasser has a phenolic spacer between the carb and adapter for the same purpose.