[markbvt]

Be aware that whenever you make any change to the engine's intake or exhaust, you're going to end up with a different air/fuel mixture. In this case, the real question is, what sort of exhaust are you replacing with the Muzzy? If it's a similarly open exhaust, then you may not need to rejet. If it's the stock exhaust, you probably will -- but chances are you'll be fine just stepping up five points in main jet size (so, if the stock main jets are 120s, you'd go with 125s).

Quick primer: most modern CV carbs have two replaceable jets (main and pilot), a needle, and a pilot screw (aka the mixture screw). The pilot jet and pilot screw control the fuel/air mixture from idle up to about 1/8-1/4 throttle; the needle takes over from about 1/8 throttle to about 3/4 throttle; and the main jet takes over from 3/4 to wide-open throttle (this is a rough guide -- the ranges actually overlap a fair amount).

Typically, one starts the rejet procedure with the main jets. Install your new pipe and see how the bike runs without rejetting; chances are it'll be lean (go for a short ride, run it through the rev range, see how it feels, make a mental note of where any hesitation or rough running occurs, and when you get back home pull a spark plug or two and see what color it is -- white/grey = lean, tan/brown = good, black = rich, generally speaking). If it turns out the bike's running great and the spark plugs aren't indicating a lean condition, then great, you're done.

But my guess is you'll need to rejet, so pull the carbs, remove the bowls (don't forget to drain them first), remove the main jets, and install the new jets. Reinstall float bowls, reinstall carbs on the bike. Find the first carb's pilot screw (a maintenance guide for your bike would help, or just find a diagram of your carb model online) and gently screw it in until it stops, counting the number of turns, then back it out again to where it was and back it out another turn or so. Do the same with the other carbs. This will richen up the idle mixture.

Start up the bike and take it for another test ride. See if it performs notably better than it did without the rejet -- you may need to experiment a little with the main jet size. Also note where it feels strong and where it feels like it could be better. You may need to pull the caps off the tops of the carbs, remove the needles, and shim them (it's unlikely that your carbs have needles with moveable clips). Needle shims are just tiny washers that raise the needle slightly, thereby richening the mid-range mixture. Try a single shim on each needle first, and if that doesn't feel like enough improvement, you can always add more.

Work methodically, keep track of what you've done and what the results are, and don't be afraid to experiment a little. Rejetting carbs is not difficult, it just requires a little patience and trial-and-error. In my opinion, you'd be best off doing this yourself, not taking the bike to a shop. Unless you have a shop around that specializes in carb tuning (and these seem to be increasingly rare), it probably won't be done ideally anyway.

Oh, by the way -- contact the manufacturer of the exhaust and ask if they have jetting recommendations for their exhaust on your bike model. Chances are they do.

--mark