72 Demon starts bogging sporadically once warm

So it has a regulator on it that appears to be new, same with the pump and tank honestly. After crawling under it last night though I noticed on the tank that the P.O. messed with the tank. It has 4 vent tubes on the side. 3 of them are pinched closed and the one left open has a 4” piece of hose pointing to the ground (dumps fuel out when tank is full). Then Coming off the sending unit, there’s two nipples. One has the fuel line attached to it going to the pump mounted up on the frame, but the other one has a short piece of hose that has a bolt in the end of it to block it off......

Anyone have any idea the correct purpose of all those blocked vents or a diagram of what they SHOULD look like when properly used? Or any idea if that’s the culprit? Thanks again