Are you using an electric fuel pump or mechanical? Have you checked your fuel pressure? Which carburetor (or FI) are you running? Are the fuel lines made with steel tubing or rubber hoses? Did you route the fuel lines near the exhaust headers? Did you use rubber insulated clamps to secure the fuel lines to the chassis?
It sounds like your fuel line is getting so hot the fuel is vaporizing. Have you tried the silver heat insulated tubing over your fuel lines near the engine? like this:
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