Next, the throttle shaft entrance on the base was machined. The machined portion will allow seals to be pressed in, keeping the fuel from getting out under boost. Without this proces when lifting off the throttle, the leftover pressure will force fuel out of the throttle shaft. People tend to think it's leaking, but the fuel is actually forcing its way out. Also, it's a good idea to spray a little WD-40 occasionally to help keep the seals fresh. With the seals in place, the throttle shaft itself has to be machined on both ends to fit properly.