A All the indications point to overly rich jetting. Short of riding the bike it's hard to tell exactly where the problem lies, although my guess would be that either the pilot jet or the needle jet (if it was replaced) are too rich. But those are just guesses, the jetting might well be too rich across the board, or it might be something as minor as an incorrectly adjusted pilot screw. There's even a chance that the float level setting is off, or a vacuum or vent line pinched. I'd start the diagnostic process by determining exactly where the bike is running rich. If it's just at a particular throttle opening, try leaning out that carburetor circuit. If it's across the board, a return to the stock jetting might make it easier to fine tune things because you can change one jet at a time and see exactly how it affects the bike. Lastly, since most of your riding is probably at relatively small throttle openings the first place to start is at the pilot jet, try leaning it out with the mixture screw. If things change for the better you're on the right track.