What kind of fuel are you running? Bored or stroked? High compression?
Are you getting it from Shell? If so, stop. I chased this same problem you describe. Switching fuel from Shell gas made the biggest improvement, as troubleshooting and adjusting jetting is next to impossible if the fuel is no bueno or even not consistently used to tune and run on. Also check your hot start cable at carb for good seal and that it closes all the way, especially when turning the handle bars.I got 91 octane in it best I can find for it as they dont sell 93 octane here.