I'd have a good look at your carbs, if they haven't been gone through, it may be time to replace the needle jet, and all of the seals and gaskets and possibly the rubber diaphragms, check/adjust the float level, and condition of the floats, and the float needle rubber tip, and perform a thorough cleaning of the drilled passageways .
Check your 'choke' cables for proper adjustment, so the 'choke' isn't operating when you don't want it to .
Another remote possibility, how accurate is your odometer ?
When you refuel, do you fill it to the same level each time, like the bottom of the filler neck, with the bike on the center stand .