Try this, but get somebody to help you. This is a great trick!
Remove radiator cap, then carefully lean the motorcycle over to the left as far as you can, Raise back up straight, top off radiator, then lean all the way over to the left again, as far as you can, if possible, almost to its laying on its side!!!!!!! Then top off. Continue doing this as long as it continues to take water/antifreeze.
The crux of this story is its almost impossible to get all the air out of the system. Did you recently change or flush the system? Was it fine before this? This method does the trick. Allows all the air to surface to the Radiator cap opening.
Now, in 1992, I had a racer in Savannah Georgia one Saturday ask me to help him with a overheating problem on his 89 ZX7 race bike.
It sure only took a couple of laps to overheat and pour boiling water in the reservoir tank. I checked for all the usual problems, such as mechanical problems etc. All checked OKAY. The problem turned out to be that he had removed the shroud around the radiator that acts like a funnel pouring air into the radiator and all the little plastic pieces in the fairing. We reinstalled all those little plastic pieces, and PROBLEM SOLVED.