Re: Vapor lock
Bruce, Tom. This is simplistic, as I have no knowledge of what the details of a Model A are.
I believe "vapor lock" is a relatively rare occurrence, when compared to the number of times the term is used. I think it occurs when a portion of the petrol between the fuel pump and the needle valve changes from the liquid to a gaseous state.
A negative pressure in the tank, cause by a blocked vent is not vapor lock.
A bubble of gas caught between a carb and a gravity feed tank is not vapor lock, its an air lock caused by the run of pipe not having a suitably consistent gradient. I say that because the bubble would run straight up into the tank, and be replaced by more petrol, if the pipe was correct.
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