fuel tank wont fill up

I have a 2005 kia optima, 70000 miles on it, I was having trouble filling up the gas tank as the pump would stop before its completely filled up. I found out that If I pull the rubber back from the pump nozzle and let air in while pumping gas I can fill it up. Does anybody know whats wrong. are the fuel vents clogged? if so how do i fix it? or is something else causing this?

There is a filter for your charcoal canister that can be plugged also the close valve before the filter may be stuck.

The canister is located behind the LR wheel.

I have a problem with mine overfilling. When it gets full and kicks off the pump, gasoline pops out and rolls down the side of the car. Plus, there is a fuel smell afterward inside the cabin until some of it burns out of the tank. It just started doing this a few weeks back. Now when I fill up, I have to control the output of the pump so it doesn't overfill.

Could be the same problem still. Most likely its the closed canister valve/filter. You might have a cobweb in the hose that the CCV exhausts into. It goes up the filler neck, you can blow it out from underneath with shop air to make sure there isn't a cobweb, otherwise you will probably need a CCV and filter.