Gotta question - Where does the air come from that is in the fuel pump dome?
It's probably not "air"- - -it's vaporized fuel. A little vacuum on a very volatile liquid like gasoline is bound to make a little of it evaporate. That's what happens when a pump "vapor locks"- - - -there's not enough pressure provided by a weak pump to overcome the tendency of the fuel to boil in the pump and the line to the carburetor as the engine gets hot. Once a large volume of vapor accumulates, the pump stops moving liquid- - - -it's just pulsating vapor. The old practice of putting wooden clothespins on the fuel line and/or wrapping the lines with aluminum foil is simply adding an insulator to help keep the lines cool.
Jerry
