How do I stop vapor lock?

67Dart273 said
The reason a REAR mount electric pump can help over OEM is that the feedline is not under a vacuum. The pressure in the feedline with the pump in the rear raises the boiling point of the fuel. There of course, are limits.

"So far as the cap" remember that NO FACTORY CAP provides the vent function. In 69/ earlier cars, the vent was near the top of the fill tube.

In 70 cars with evap, and later, the vent was the 1/4 line to the front, and either that must be kept open, or else something else to replace it as the vent

The evap equipped cars ALL had what are called "pressure vacuum" caps, which allow "some" pressure to build, as well as "some" vacuum to occur, before "relieving" thepressure.

These are a PITA because changes were made over the years. There's a couple of threads on these caps

Here

http://www.forabodiesonly.com/mopar/showthread.php?p=1970887599

Agreed on all points. The pump should be located as close to the supply as possible since most all pumps, electric especially, don't suck very well, and pressure is pressure. The regulator should be as close to the carb as feasible if it's going to help with boiling.

On the cap, it shouldn't matter unless things have been modified over the years, or you're unsure of the presence of any vent. Some get capped by well meaning previous owners, some get clogged.. And finding a proper cap is a pain. That, and it's only a remote possibility that can be tested by popping the cap open IF you have issues with it staying running down the road.

Sounds like that's no longer a problem though, but duel supply at WOT might be. The improvement after rerouting the hoses points to one of the problem being the heat applied to the line when warm.