There is only one vent to the tank in 72. That is the small 1/4" line coming up front. You need to determine if it's open, and there is a ball valve right near the engine end supposed to prevent liquid regurgitating up in there. If you are not going to use the carbon can, I would cut the line back to get rid of the ball, remove the cap and blow through it to clear it and make certain it is clear
Is all the plumbing properly connected back at the tank? You need a shop manual to see this, download one at MyMopar
You can run (hose if necessary) the 1/4 line "up high" in the engine bay and then turn downwards or you can plumb it into the outer bonnet of the air filter
Screenshot right out of the 72 manual. With the carbon can disconnected, this is what is important...........what is in the circle IS YOUR vent
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