Can't get gas into the tank, acts like it is full, but it is empty

I'm working on my dad's old 71 Duster. I'm running into a weird issue, I can't seem to get fuel into the tank. When I try to put fuel in the tank I get a little in the tank, then the filler tube fills up and fuel runs out. I know I get a little in the tank because the car runs for a few miles before running out of gas. We've tried multiple times, both using gas cans and at a gas station. It does have that evaporation system tube in the trunk could that have anything to do with it? I've also tried threading a small hose down the filler neck to see if I could vent it, that didn't work. Tried pumping fuel in through that line into the tank, that didn't work either.