Go Tech engines are shimmed for 30% nitro out of the box. To help ease the break-in process, intall the extra shim to help turn the engine over. Most people leave that shim in until the hit the 1-1.5 gallon mark. Once you are finished with the break-in process, keep the tune slightly on the rich side of a race tune until the pinch is gone. Once the pinch is gone, then you can race tune to get peak performance. Good luck.