I know someone who did it on a CR125 carb. He did both sides, but didn't do much. He is a certified Honda Tech also. He tried to explain to me, but I'm not sure if I caught it all.
Make sure you measure as you cut, but don't cut too much. He said that you could only cut so much becuase of the slide. If there was too much space below the slide, it would not run right.
He said other than reeds, this was the best mod he did...
EDIT* I can try to get some directions on how he did it.