Don't forget to leave some extra slack in the sheath/outer tubing as you'll need it when turning the motor.
I used to set up the cable length by turing the motor to the direction where you need the most length. Turn your radio on and open the throttle fully then while holding it there, shut the receiver off. Open the carb all the way then fasten the screws or whatever your setup is using and that should put you right in the neighborhood.