You need to remove your air cleaner and look into the carb opening while moving the throttle on the controller. The servo should not open the throttle past the point where you see the carb fully open...that is where you either set your trim, or set the servo throw...whatever. Not sure if the stock transmitter allows for end point adjustment but if not, set your trim on the controller to the center, loosen the collar on the control rod and when the throttle is fully pressed, tighten the collar so that the carb is right at the point where it is fully open, that way you cannot open it further unless you play with the trim knob.

When you have this set, adjust your brake rod to just barely engage when the throttle is closed and when it is slightly giving pressure on the spring. That way the travel it has against the spring is soley for the brake.