pilot jets in the carbs, mines has done it twice now, i know its an ass ache but will be worth it when you overhaul the carbs, she will be running smooth again, i need to strip mine down again as it hesitates at 6k occasionally
hope it helps
i am also having this same issue i have cleaned the carbs, new plugs, fresh gas. it idles ok runs great after getting past the bog. i will be taking the carbs back apart again to see if i missed anything but they were clean to start with. i will let you know if i get mine fixed and maybe it will help you out
If you aren't fermiliar with carbs, even the smallest impedance in flow from the jet will cause a condition that isn't ideal. It takes very little to gum up a carb jet. Just replace the jets with the same that came out.