fuel tank lines?

67Dart273 said
Don't use it for a return or plug it unless you make other arrangements for a vent. That 1/4 line --which went to the canister--IS THE vent

As said above.......you can go to MyMopar and download service manuals. These systems changed over the years.

1....Nothing before 70 had them, and only some 70's, CA state notably

2...I think but not sure that 71/ later all cars had it

3...First few years they used a big long tank up in the trunk, "vapor separator."

4...Later years incorporated this function into the tank itself, so no separator in the trunk

5....Pay extra attention to fuel caps. They changed in the years with these systems. "Somewhere on here" is a thread on the different caps

Exactly this. Here's some more in depth info. Courtsey of @slantsixdan

For '72, things got very much better. At the back of the car, the inner tank was deleted; by clever shaping of the top dome area of the tank, the same function was achieved by means of a controlled air pocket at the top of the inside of the tank. The '72+ tanks also have only one vent fitting. At the front of the car, the crankcase was no longer used to contain fuel vapors. Instead, a canister containing activated charcoal granules was mounted at the front corner of the engine bay. Lines lead to it from the carb bowl and the fuel tank vent. There is a purge valve mounted atop the canister, with a small diameter vacuum line teed into the distributor vacuum advance line, and a large diameter line from the underside of the purge valve, teed into the PCV valve hose. There's vacuum in the distributor vacuum line only above idle, so the purge valve only opened above idle. Voila, no more hot start/hot idle problems, since fuel vapors were only drawn off and burned above idle. This system works fine.

As for the gas cap. The stock gas cap is not vented. It is a pressure/vacuum fill cap. Here's the excerpt out of the manual:

And some more info courtsey of @slantsixdan

A-bodies do not use vented caps. The car needs what is called a "pressure-vacuum" fuel cap. It is vented, in a manner of speaking, but it's not the same as what is commonly referred to as a "vented" fuel cap. A vented cap has a passageway for air to flow in and fuel vapours to flow out. A pressure-vacuum cap also does, but has two spring-loaded check valves -- one very low-tension one controlling inward flow, and one high-tension one controlling outward flow. Pressure-vacuum caps were first used in '70 on cars sold in California, then in '71 throughout the US and Canada. The design of the cap was changed in the middle of 1971 production. The cap for your friend's '72 Scamp is a late-'71 through '76 item. The '70-'71 cap will not fit correctly. A pre-1971 (pre-1970 California) cap is unvented and will not fit or work correctly.

On my car, 72 scamp, that line is just cut off shortly after the metal pipe in the engine bay. It's never cause me any problems. But it's on my list of things to fix. I am probably going to either use it as a return line when I do my EFI and vent the tank differently. Or leave it as a vent with a filter of some kind. I'm not sure which way I am going to go yet. But am leaning towards turning it into a return and venting the tank differently.