gsxr 750 carb problem

[Cangix]

Question about air/fuel adjustment screws. Only one carb out of the four will allow me adjust the air/fuel needle (clockwise effortlessly) to the point where you can see the tip of the needle protrude into the bore of the carb (see pic).The other three wont allow the same amount of needle adjustment?, and yes they are all clean inside the holes. I am thinking all of them should be the same????  Has anyone ever seen something like this before?

[Gixer1460]

Compare two different screws for the taper - the odd one is probably a rogue replacement!

[Cangix]

UPDATE!  I bought a tap to clean out the threads, thinking there was crap down there, and wouldnt you know it!