First, Adjusting the carb will not Affect the SOUND. Thats all in the exhaust.
NO, I wouldn't take it back to the same mechanic. I might give him the bill for the repair, though..
Having the carbs, "Worked ON", is meaningless? What, exactly, did you have done to the bike? What parts were replaced and why? have you bothered to LOOK for a potential cause, you now hose that got left off, leaking carbs boots, loose electrical connection, ect?
93 VT1100C Harley Killer (1150cc), VH Exhaust, 2mm sleeved and bored, Modified Heads and Valves, Adjustable Timing, Touring Seat, Baby Apes, Metzlers