Chinese JS250 atv trans problems

Have a chinese brand atv, very similar to the Jianshe js250 (250cc)
Atv shifts into D, but when you give gas doesnt move, and makes loud sound... took apart, diff, and driveshaft look fine, could it be the clutch?Output shaft? rear end? The point where drive shaft connects to on the engine/trans, doesnt seem to spin properly when u give it gas, seems like something is cause it to jam but when the wheels are not on the shaft or no load, it spins fine... also my reverse doesnt work...

Motor js250 roketa/jainshe/sumoto