Your ride is a 66 right? There's most likely no vent on the tank to early,but the gas cap should be vented.so you need a vented cap or your now vented cap is bad.replace it.
That's my guess
You definately need a vented cap. Ask me how I know. I got drenched with fuel ine hot day last year when I removed my cap. The vent had rusted up or clogged. Should vent both ways. It is baffled.
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