Turn the mixture screw all the way in then back it out between 1 1/2 turns to 2 turns
that will get the engine to idle from there set the idle speed with the throttle screw to desired idle rpms
now turn the mixture screw in slowly until you see/hear a fall in rpms
now screw the screw out until again you hear /see a fall in rpms.
half of the number of turns back in from in to out will be the desired air /fuel mixture setting
adjust the idle with the throttle screw if it has altered
you can repeat the procedure again to fine tune the mixture after adjusting the throttle screw