I guess I'm not understanding the reasoning behind why I had a charcoal canister AND a vented gas cap...I mean why put an emissions device that prevents hydrocarbons from venting to the atmosphere and then also have an exit for them in the gas cap?
The cap is for pressure/vacuum relief. The ECS is for reducing emission of fuel vapors. 1972 was the first year for ECS. You don't "need" the ECS system (emissions only) for performance, but the extra vent line that was connected to the charcoal canister helps when your filling the tank with gas because it gives a pressure relief point when your pumping the filler neck full of gas and the air in the tank can't escape. I'm not a gas tank expert, this is based on my experience.