The 2016 MXU or Mongoose 270's have an age 14 restriction. They are restricted to be able to qualify for use for 14 year old and up.
There is a bulletin put out by Kymco USA that instructs you on how to "De-Restrict" the unit properly.
But, this de-restrict does not allow you to fully unscrew the throttle stop.
If you have unscrewed the throttle stop and it is restricted or De-restricted per the bulletin, the unit will over rev, overheat and eventually smoke the motor.
My recommendation is to order a variator shaft from a 2012 MXU or Mongoose 300 and install it.
Then you can run the bike with the throttle stop al the way out if you like. It will then run just like a MXU or Mongoose 300.
Have fun.
CJS