Axle play at Front differential & bearing whine #%&*

[SinusoidalTendencies]

curious where to get the mixture screw as i'm remembering mine has a scored ring a wee bit down from the tip and no one said anything about it when i mentioned it in a previous post. any info on it's function and what would entail damaging it to the point of not functioning correctly will be appreciated as well. my current understanding is that it holds the lower valve open a wee to allow an idle.