The one I had most trouble with had me so annoyed, that I completely disassembled it right down to removing the jet block. I figured, what else do I have to lose....it was only then that I could see quite clearly that a section about a quarter to a third of the needles seat area was missing, which made me think that because this is an air adjusting screw not a mixture one, like on a TT that it must be getting far more air even with the screw wound right in, than the correct balance of fuel to match it. I could not see how I could fix this easily, and especially since it was a NEW carb, so I returned it to Burlens, and after months of continuous phone calls, they told me that they could not fault it. I found this very hard to believe.....So when I finally got it back and installed, I had already modified the slides to my own preference and it seemed to adjust up and run ok......This is a real pain in the a--se seeing as the new 276 carbs seem to give good results straight out of the box....Go figure.....anyway this should give you an idea as to what you may find. Like most things on a Vincent, there is always something to "Fettle" before all is well, Cheers.........Greg.