Those symptoms are of a bad fuel pump. Chinese fuel pumps are notorious for this. Best to replace it with a real Mikuni fuel pump.
http://www.amazon.com/Mikuni-Genuine...kuni+fuel+pump
Scooters with the tank in the floorboard need a vacuum operated fuel pump to pump fuel up into the carb. The Chinese ones simply can't pump with the reduced vacuum of high rpm running. The Mikuni's can.
Best thing to do is a desmog since these scooters benefit greatly from that. Then get a new fuel pump and run it on it's own dedicated vacuum line to the intake manifold that's as short as possible and has no T's. It shouldn't if you desmog the scooter.
Those two things thing usually solve the mysterious high speed bogging issues people experience.