Hyundai Repair: 2002 HYUNDAI ELANTRA GAS PROBLEMS, hyundai elantra, charcoal canister

Question
WE BOUGHT THIS CAR USED 48,000 MILES THE CHARCOAL FILTER IN FUEL TANK OVER FLOW HAS BEEN REPLACED TWICE KNOW ON OCCASIONS WHEN WE PUT GAS IN IT IT WILL SPIT ABOUT A GALLON BACK OUT OF THE CAR.  WE STOP WE THE PUMP CUTS OFF SO OVER FILLING IS NOT THE ISSUE.  ANY SUGGESTIONS?  I THANK YOU IN ADVANCE FOR ANY HELP YOU CAN PROVIDE

Answer
If the pump fails to cut off when the tank is full, then the problem is with the fuel pump.  In that case, you should seek reimbursement from the gas station for your repair expenses.  When this occurs, I'd expect that you get liquid fuel in the charcoal canister, which will ruin it.

If the fuel pump shuts off prematurely before the tank is full, then there's a restriction preventing the air from exiting when you fill the tank.  Although the canister is one place this could occur, the restriction could be in the fuel tank, in one of the valves in the top of the tank, in the hoses connecting the tank to the canister, in the canister filter, or a stuck closed canister close valve.