225 Slant needs a good idle. what rpms are you spinning?

Idle mixture screw setting for best running is gonna vary a bit engine to engine. You can tweak out a carb and get it running absolutely great on an engine then drop that carb on another engine and there's a good chance you will have to tweak it again to run it's best on the 2nd engine.
I usually set them around 1-1/4 to 1-1/2 turns from lightly seated to start off with. And from there? "Whatever works" for that particular engine