There is really no such thing as an initial setting for the idle stop screw on that carburetor. It is not a mixture screw. It is simply a 'stop' which the slide sits in top of when in the down (idle) position. Its only purpose is to determine the idle speed by virtue of holding the slide up (open) a very small amount when you have completely let go of the throttle twist grip. Screwing it in causes the slide to go up slightly thus increasing the idle speed. Turning it out does the opposite. Just set it to get the idle speed you want. That's all there is to it.