Vapor lock issue?

David Eldridge said

Sorry not air pocket, vapor. I think its just boiling all the way up the line to the carb.

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You are correct. Its vapor and the vapor pressure can exceed the pumping pressure. Since its a flow situation, liquid fuel that contunes to be pumped into the local where vaporization occurs will continue to block the flow of liquid. This can happen on either suction or pressure side. (In fact you can measure the pressure in the feed line to determine where the problem lies.)
Hot Fuel Lines
One more form of vapor problems was/is pushing liquid fuel in front of it into the carb bowls. Chrysler dealt with this at several times including the use of fuel pumps that had a tiny return bleed built in.

The engine often can continue to run at low power because there is sufficient fuel in the bowl (and vapors going out the vent into the air cleaner). When more power is needed, it revs and dies until the throttle is closed enough for the engine catch.

Realize the fuel is not completely boiling. Unlike a simple fluid like water, there is a wide temperature range which vaporization occurs. Winter fuel is allowed higher Reid Vapor Pressure, which can be a real problem when the weather turns hot.
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