I would try running it in the reserve position, if that seems to cure it, check to make sure you have more then a quarter of a tank. Depending on the year of your bike or the emmisions it's built for (CA?) would change the venting configuration of your tank and carbs. I don't know where you are at or if the bike has set for a day or two. At this time of year when something acts up on me, the first thing would be to check vent tubes. Most of our bikes have one going to the right ear (not fully inserted, just held there), some of us just have it open between the carbs. It wouldn't be the first time a wasp has tried to build a nest in one. I've seen it on more then one truck that starts blowing axle or transmission seals, same thing, they have to vent.