Sputtering when accelerating

Hi everyone, I've got a 1983 mk1 GTI tintop. It's been running absolutely brilliantly for years but recently started sputtering when accelerating. I changed the fuel filter changed the spark plugs cleaned the points adjusted the mix as it was quite rich and adjusted the idle. It seemed to solve the problem but it started again but not as severe as before. What could it be? Should I get a new fuel pump but I can hear it prime when I turn it on. I have got a boroscope into the fuel tank and seems to be ok, the filler neck is not crumbling. I'm at a loss, it's got to the point where my mrs wants me to get rid but I just can't do that lol. Any help will be greatly appreciated