Are you saying that your throttle cable is hanging up? Check for sharp bends in the cable, and try to route it so that it makes large bends, rather than sharp ones. Squirt some WD40 where the cable goes into the housing, at the throttle grip, and work the cable back and forth. Make sure your initial settings on the carb screws are correct.
Looks for places where the outer cable housing is broken; that can make the cable hang up. The cable might be frayed somewhere, which will make it hang up. In either case, get a new throttle cable from your Yamaha dealer...
The QT only has one gear. Change the gear oil, and if that doesn't do it, you may need a new clutch.
I've only had my QT for 3 weeks now, and I'm still dealing with my own problems with it, so I can only offer general mechanical advice (experience with VWs, none with 'peds)... Seems like a solid little bike, though.
'84 Yamaha QT50