lemans 2 carb mixture screw

I am confused. From reading various manuals and speaking to various people I am unsure what the mixture screw is doing on my carbs. The screw is on the engine side of the carb and I understood this meters fuel not air. Therefore winding it in closes the fuel supply thereby making the mixture more lean. Where carbs have the screws on the intake side of the carb they meter air and therefore screwing out increases air flow making it run more lean. Is this a general rule, am I right in this appraisal, have i got it all wrong and how important is it. My V50 2 has a similar screw position on the engine side but I was told recently that unscrewing it makes the engine run more lean. Hence my confusion. I tend to check plug colour and trial and error. Had thought about ‘colour tune’. Any thoughts?

Yes I’ve heard if this if it’s downstream or upstream etc., as well, I think you’re right it mainly controls fuel, screwing out increases it and vice versa, BUT air is mixed with it via a gallery from the intake so is a bit of both. But screwing out enriches. By the way optimum position is typically 2 - 2.5 turns out, not 1.5 as the manuals say which is a starting point for setting up. Then screw out until it idles on the stops. Haynes says from this optimum, screw in until revs drop then back out to restore the revs to normal idle, do for each carb in turn, BUT assumes carbs are in perfect health otherwise, and no air leaks etc.