What causes the problem slow filling fuel tank on a 1999 Daewoo Nurbria?

Hi, I had the same problem as you. In my case it was the previous owners fault. For some reason they had disconnected the fuel filler pipe from the fuel tank; and did not replace it carefully enough. There is a rubber seal which can get forced out of position and cause a blockage in the filler pipe. I found this as mine also leaked fuel when trying to fill the tank as well. Hope this helps.