I'm running a 270 main in the stock carb,, stock pilot, stock needle position, airscrew at stock position 1.5 turns from bottom. Motor runs just right, not too rich not too lean.
Mods are: FMF Gold series pipe w/shorty silencer, modded airbox lid (hole cut, prefilter installed, and removed snorkel), pro design intake manifold, billet reed spacer, TORS removed, oil injection removed, 32:1 mix.
Stock Porting, Stock bore, stock timing, stock reeds.
Have you checked the airscrew on the bike since you've owned it? Some people mess with them without knowing what they're doing. If you're not sure about it, turn it all the way in, then back it out 1.5 turns, then adjust from there. Turning the screw out (counter clockwise) leans the mix, turning the screw in (clockwise) richens the mix, if it runs best with the screw all the way in, go to a bigger (richer) jet and re-adjust.
My only other suggestion at this point besides getting the right jetting is tear down the carb and be sure it is spotless. A small obstruction in the pilot jet or the main nozzle, though not likely the cause of your problem, may be a contributing factor.
Good luck.