The stock setting for the 21BB are kind of rich, but are a good place to start from. As with any engine, the needles will vary from place to place. I'd recommend doing a search for 21BB, needle settings and tuning. There have been may posts about tuning the 21BB and alot of methods outlined.
One important thing to remember, never touch the mid range needle (unless you're taking the carb apart for some reason).
Get it tuned for high speed then start working on the LSN. Do the pinch test to get that set. (good search phrase) Then retune the HSN after adjusting the LSN, and then check the LSN again. A couple times of this and you should have it set.
The 21BB isn't the dog that alot of folks claim it is, but it's not an outlaw 26 either. It's a solid mill that will motivate a savage.
Whitt...