You can try turning in and out the mixture screw under the carbs, have a read/search about what the mix screw does. Not just on here.
Make a written not of exactly how many turns in to stop (dont screw it too tight!) so you can always go back.
Screw in = lean
Screw out = richer
This is only on the idle/low speed circuit.
If you make it too lean the engine will run hot (bad!!!!) and the spark plug will appear white.
Stock set up with stock muffler is 2.5 turns out from stop. (ie screw it in until it stops then screw out 2.5 turns) I'm stock and theres a difference from 2.5>3.2 make it smoother for me. I've heard that with aftermarket exhausts people are going out to 5 turns.
If in doubt take it to a dyno, pref one that deals with single cylinder bikes.
Heres information about a carb set up you can do
http://web.archive.org/web/200212050740 ... RBMODS.HTM Kit you can get to set it up
http://www.off-the-road.de/en/Other-bik ... stiff.html Theres also another one you can get from a german website which I cant find right now.. Anyone else ?? Bernd something or other???
Remember setting up carbs can be complicated and frustrating, so read first and choose wisely. (make notes of what you change so you can always easily go back with no guessing!!!)
Good luck.