The factory specification is 6.2mm to 8.2mm (0.24" to 0.32"). This is measured from the gasket surface to the top of the float when the float just contacts the needle without compressing the spring.
Before beginning, ensure you have a clean workspace and a carburetor rebuild kit containing fresh O-rings, gaskets, and a new needle valve. mikuni bds26 service manual
Unscrew the four Phillips screws. Be careful not to strip them, as they are often soft brass or zinc. The factory specification is 6
Turning the air screw clockwise decreases air (richer mixture), while counterclockwise increases air (leaner mixture). Troubleshooting Common Issues mikuni bds26 service manual