It would help to know the capabilities of your transmitter. EPA/Travel Adjust? Throttle curve? But generally I find it best to set the servo(using the transmitter hopefully) to mid-travel or neutral. Then connect mechanically to the throttle arm of the engine so that the carb is half open. Then using EPA/Travel Adjust set the high and low throttle position. Then if you have throttle curve, run the engine and set throttle curve to give the desired engine speeds at various throttle stick positions.