I am in the process of restoring the fuel system on my '71 Fury. My car had the problem of when it got hot, it wouldn't restart. Fuel delivery issue, tank not venting. In the process of dealing with the vapor separator tank, i noticed it was very rusty inside. I cut open the back of the tank and cleaned the 4 gas tank connecting tubes. the 5th tube with the 90 degree bend, it goes to the crankcase breather on the passenger side valve cover. It has a small orifice inside. I tried to blow it out with 90psi from my blow gun. Totally clogged with rust (explains the fuel delivery issue i was having.) Removed the tube from the tank with a torch, Ran the smallest drill bit i could find through the orifice. Blew through it with compressed air. Good to go. Soldered it back in. Used the POR 15 fuel tank sealer kit. Dunked the entire vapor tank in the metal prep, then once rinsed and totally dry, used a very small funnel, ran the sealer through each tube, then poured some in the tank itself. After it cured for 4 days, i soldered on a new sheet metal patch on the back. The POR 15 sealer worked well, as there were no leaks. Rechecked all 5 tubes including the orifice tube with compressed air, all clear. Now when i do final assembly of the new gas tank, sender, and lines, the vapor system should function correctly.
To recap, check that orifice tube if your tank is not venting.
Hope this helps!