What is the purpose for 4 Vent Fuel Tanks on my 1974 Plymouth Barracuda?
Any benefits for or against?

wow that's cool seeing inside.
Ok thanks so much, i will use the 4 vent tank.

I've known some guys use a inline fuel or air filter to get rid of that huge tin can in the wheelwell

P.s great photo! I wondered where they went in there

Actually the Barracuda has something like a long twinkie shaped can right in front of the tank. Nothing in the wheelwell.

My 72 Imperial has the external vent manifold. The difference I see is that it has one hose that is larger than the others. I'm not sure why they decided to make that tube larger.

The liquid/vapor separator all part of the sealed evap system. As was said the line going up front either goes to the crankcase thru the breather cap or to a charcoal canister. Its really not a bad system but if you use it you have to run the line up front to the crankcase or a charcal canister or you can smell gas on hot days. I used to get cars from the body shop where the customers complained of gas fumes up front as almost every time it would be a cracked charcaol canister from the front end damage. Dont forget if you run the canister and the closed system its made to work with the sealed press/vacum cap. I dont run the charcoal canisters on my hotrods. But that is a nice tank vent system. Ron

Are the charcoal canisters repopped? Parts stores or vendors? Or can you adapt something from other vehicles?

You guys said that the line that terminates in the engine bay up on the inner fender should be connected to the charcoal canister. Is there a line that runs from the canister to somewhere else? Or is that the end of it? I have mine connected to my air cleaner with a hokey little setup. I don't have a charcoal canister but would like to install one to help with a fuel smell issue. Pics would be great. Sorry, don't mean to hijack.

Thanks,
roe

All the canisters I replaced were from the Dealer I worked at. I have not seen them aftermarket but you could always try a place like Auto-Zone or one of them stores to see if they sell any.
The charcoal canister just stores the fuel evap fumes until they are drawn into the intake to be burnt in the cylinders. Most of them have a type of control valve so they dont pull the fumes at the wrong times as most purge the fumes when at cruising speeds. Some of the control valves will use ported vacum to turn on the valve that has manifold vacum to purge it and alot of cars use a solenoid controlled by the PCM to purge the canister. Thats because you dont want it to purge fumes at idle or on decell where it would go rich and could stall. The newer Mopars even have addaptive fuel memory cells that compansate for the fumes when purging. Ron