Gas carbs such as Walbro carbs don't have a linear throttle response to the butterfly opening / travel. So a good mechanical setup is needed that will open the butterfly accordingly and provide a linear power response. you also will find that a gas carb reaches full rpm long before the butterfly is open the full 90 degrees. this is normal and nothing to be concerned about. Servo arm length is very important, either being the same as the carb arm or slightly longer (up to 1,2 times) is OK.