If the motor will go to full, but then slows down to 1/2 or so without you moving the stick, it sounds like your speed control may be bad.

As far as startup is concerned when you've just turned on the system, you have to move the stick to full, hold it there a few seconds, then retard the throttle to idle. The speed control will be armed.

If your speed control's bad, it needs to be sent in to the service center.