d. Set the idle adjusting needles to give the highest steady manifold vacuum reading, or the smoothest running and maximum idle speed if no vacuum gauge is available. This can be accomplished by turning one idle needle in until the engine begins to slow down, then backing the needle off over the "high spot" until it again begins to slow down. Setting the idle adjusting needle half way between these two points will provide a satisfactory idle. However, best performance will be obtained if the idle mixture is slightly on the rich side. Adjust first one needle and then the other. After the idle mixture has been properly adjusted it may be necessary to reset the throttle stop screw to the specified rpm.