Is it more like anything more than 1/2 throttle and it cuts out? If so, possible main jet problem. Raising/lowering the needle will only effect the throttle from 1/2 to slightly below 3/4 throttle, after that its all main jet. I would try that first. If the main just dosent cure it, it may be an ignition coil problem, I have been here before.
THE 80's RAGE! Currently owns:
81, 85 Yamaha Tri Moto 125
83 Yamaha Tri Moto 200 x2
82,83 Yamaha Tri Moto 175 project
85 Yamaha Tri Z 250
84 Kawasaki Tecate 250
84 Honda ATC 70
85 Honda ATC 350X
84 Honda ATC 250R
(2) 84 Honda ATC 200x
82, 83 Honda ATC 185s
81 ATC 200
Lots of other parts and bikes