As others have said... Believe that's an AIR adjusting screw. Fuel is metered via passageways and meteriing jets. The volume of iar mixed with that metered fuel is adjusted by this screw. Out leans it down by allowing more air in the final mixing stages of that carb.
Usually if an idle mixture screw meters fuel it is long and slender. If it meters AIR it is rather blunt with a steep taper. Like the difference between a drift punch taper versus the taper of a cold chisel grind.
Either get it running & back it out a couple or three turns to see what it does or look at the old one (from your kit) & see if it isn't a blunt nosed goober! If blunt nosed... back it out a couple or three turns & see what it does. Mine 3020 has a MS carb or I'd just look for ya.
Hope that helps.