If you try to screw the idle mixture adjustment in too far, it will fall out inside the carb. It gets installed from the inside. Please see page 23 of the manual for initial setting. You can also set it by looking into the carb and having about a 4-5 mm gap between the needle and the nozzle when the carb is opened to the full throttle setting and you look into it.

Starting off with the idle mixture set to "stupidly rich" works well. You start the engine at 1/4-throttle or so, advance to full throttle and get the high-speed needle set, and then retard the throttle to work on the idle RPM and mixture. Any idle below 2,500 RPM or so is considered "good".