Thanks everyone.

right out of the box, I only did the setting for carburetor, which was 3 turn (from the manual), but then I felt no power when I hit the full throttle, so I I turned to 2,5 turn (I got this from the forum).

is there any connection with slippery clutch? maybe to tight.
or, the differential backlash, I think it's too big. the backlash is about 3~4 mm.

Thanks.