screw adjustment on Carb (250 Race)

[mrdavies]

Hi
How far out should that (brass) screw be turned out on top of my carb... ?

I have the race 250. I assume that this is the fuel / air mixture.

Im not sure how to properly adjust or set it... ?

I will start by turning it all the way too the right ... in this position is this more or less fuel ( lean or rich )

Thanks