You're probably not going to find the answer here (they tend to reject these kinds of questions). I suggest you pick up a copy of just about any Harley-oriented magazine, such as American Iron or Hot Rod Bikes. Looking back in their files will provide you with info.
For the Sportster, check out the Archives and FAQs at:
Basically, the carb should be good for most exhaust modifications. When you change the air cleaner, however, you will want to richen the mixture substantially. The carb tuning is dependent on intake, exhaust, timing, ignition, etc. It would be difficult to tune for exhaust changes only, unless you did it on a dyno. Then, it's more trial-and-error than calculation.
