You can find alot of links of real carb tuners advising against drilling the slide.
http://carbjetkits.com/drilling-carb-slide.html <-notice he says it can cause a hesitation at the bottom.
http://www.cv-performance.com/harley-cv-carburetor-tuning-issues/ <-scroll down to 6 and ken talks about over drilling the slide. If you do searches on the harley forums about drilling the slide they all advise against it. You know harley uses the same cv40 carb as ours except without a carb warmer. And these guys tinker even more than us with carb settings and dyno tunes etc... I have heard it from some vulcan 1500 owners as well, It wont let me post a link from the archive at vroc.com but here is the quote :The 1500 reacts to the slide being drilled in a very negative way in my
opinion. The throttle loses it's ability to *feather* the gas at really
slow speed situations like slow turns in a parking lot. It feels more like
an on/off switch than a throttle just above idle and can really be quite
disconcerting if you have the bike leaned over doing a slow turn and you try
to feather the throttle and it just shuts off and then you react by giving
it more throttle and it *jumps* out from under you. It has taken me a while
to get used to it and I would not recommend it. <-thats a post from 2003