Our old Mopar fill tubes have a divider inside, but it's just at the base.
Idea is gas goes down into the larger lower section, air comes up the smaller upper section.
The reality is, fuel can easily get into the air side at the bottom on the way down.
With fuel coming down into both sections, air can't escape through the upper section, up the fill tube, with fuel rushing down, to the vent.
If the fill tube is a straight shot down, or very short and/or low, it works.
My 62 Dart has a short fill tube behind the license plate, no problems.
Can't isolate the vent side from the bottom to the top, it'll siphon out the vent.
My thought was, run a hose down the fill tube until it bottoms out, cut it off inside the cap.
Hose has to be large enough to accept a pump nozzle, small enough to fit into the lower section at the base of the fill tube, and not interfere with the sending unit.
It would be ideal if the hose was just large enough to stick into the lower section, where it would hold it.
I think I have a spare filler neck I could check.
Also, at least on my Barracuda, it vents into the framerail, so make sure the rail is clean and unobstructed inside, or route the vent outside the rail.
