My dad has a 1940 Ford 1/2 ton traditional rod with and 8ba flathead in it. Last week we were at a show and after the truck got filled up and sat on the show field, gas started pouring out of the fuel neck all over the fender. It has an original style 14 gallon tank. What could cause this? I'm pretty sure it sounds like the vent. Also when filling up, you have to pump very slow. Does anyone have an idea how to fix this or had the same issue?