Laihyun,
If you notice that the throttle grip only moves a very limited amount, then you have a limiter installed somewhere between the throttle grip and the carburetor.
With one hand on the throttle, and while looking at the top of the carburetor barrel twist the throttle and see if it touches an L shaped bracket and screw by where the throttle cable attaches to the carb.
If you see that bracket, you will also notice the screw that is limiting the amount of movement, if so grab a phillips screwdriver that will fit the screw in that L shaped bracket, and un-screw that screw until you notice that the throttle now opens more as you loosen/remove that screw.
That is one way the motor is is governed, if the above does not work, then remove the throttle grip top cap and see if there is a C shaped piece of plastic that can be removed basically doing the same thing.
I hopes this gives you something to work with, as I have no Idea of your mechanical knowledge, But I do know That my sons AARVI A-529 (380x R1 R6 Whatever) had the L bracket on top of the carb, It was the first thing I checked when I noticed the throttle movement was way limited.
The bike wouldn't hardly pull me out of the box, then I unscrewed the limiter and YEAH!!! it actually runs great, why they would limit the throttle to that extent I don't know but it seems to be what some of them are doing... | 
Please help a noob! I just got my bike few days ago. 
