How to Prevent Holley Carburetor Fuel Boiling

Part of your problem is where you live.

100 plus in the summer and sub freezing in the winter.

Assuming you drive year around when you can the heat is great on the winter but in the summer it causes issues.

IMO if you get the coolant temp down to 190 it would help.

After that the next fix is to block the crossover off but on cold days it can be a bear when the engine is cold.

If that doesn’t fix it then you can do the return line.

FWIW at this point in time it’s almost getting to be SOP that you need an electric pump and return line.

On top of the minimal alcohol content in pump gas you have the issue that the fuel is formulated for the higher pressure of EFI.

That changes what the fuel acts like in carb’d stuff. The return line is probably the most expensive fix but it’s probably the most cost effective in the long run.