Gas nozzle keeps turning off when I try to fill up my 1991 Jeep Grand Wagoneer

Or try holding the nozzle at a different angle.

Thanks for the info. I will check into the vent line. I did try pumping with the nozzle completely upside down, but couldn't seem to get the seal for the vapor guard flush enough to the car to even get gas flowing... I'll have to try that again though, at other angles. Someone at the gas station, noticing my trouble, suggested putting a brick under the rear tire where the gas cap is (driving up onto it), to help gas flow down better, but I can't do that every time I fill up! I'd rather just do what I'm doing.

The gas already flows downward I don't believe a brick would help maybe try to look down the fuel fill make sure nothing was put down in there or dropped anything,