Just a guess on my part...an educated guess, yes, but still a guess: it is plausible that the pilot screw Vinton rubber o rings are damaged. I suggest replacing them. Replacement cvk pilot screw o rings, washers, & springs are available from CV Performance...CVP is a Harley tuner, but those pilot circuit parts on the cvk40 Harley Keihin carb & our cvk36 are the same.
The next thing I suggest checking are the vacuum piston (slide) rubbers, to make certain they dis not get pinched, punctured or torn.
