pump tweak on 300 tdi

Hi All, tried to tweak the pump a bit on my 94 300tdi and managed to turn up the "smoke screw" under the tamper proof plug ok but when i tried to take out the diaphram to adjust the star wheel it wouldnt come out and felt as though it was stuck so i didnt try and force it. I did my last 300 tdi with no problems and so would appreciate any info on what could be wrong.Thanks in advance!