[MikeK]

Originally Posted by youngd7

MikeK Fuel pump is mounted on the inside of the frame rail. I did check for flow after the pump and it was very good. Gas cap vent is working. I do have a stock glass sediment bowl with a filter in it. How would this create vapor lock?

If your pump feeds fuel at a faster rate than gravity flow to it then a slight negative pressure is produced in the tank feed line. That is why I said check for full flow at the pump inlet, not it's output.

While driving at speed there is considerable under hood heat, both in the air through the radiator and radiant, from the exhaust to the fuel line and sediment bowl. Modern gas contains a great deal of light fractions and is not designed for systems without submerged pressure pumps and all highly (25-75 psi) pressurized feed lines.

With modern gas any slight negativity in the tank feed, through elbows, valves, sediment bowls, filters, rough spots, etc. provide nucleation points for vaporization in the line when that line is warmer than the fuel itself.

Of course, your problem may be something completely different as suggested above, but I just wanted to make sure as many bases as possible were covered in your persuit for a fix! When you do find the fix, please post! Inquiring minds want to know!