I think everyone blames the carb first. I think a vacuum leak is more likely. I mean there are a million ways to get a vacuum leak. And it's not likely that the idle mixture screw all the sudden decides to move itself.
then after all that is done if you are going to do the lean drop method, basically you are going back and forth from the idle mixture screw to the idle speed screw until you get the rpms right.
best i can tell reading the 2f engine FSM. But really if you are trying the lean drop method for tuning, just put it at 2 turns out then make sure all this is done :
Be careful turning the air/fuel mixture screw all the way down. Don't tighten it at all. Just barely snug. You can damage the needle. Just touch and go back out 2 turns.
Have you checked for a vacuum leak? I mean spray carb cleaner around the base of the carb, and around the intake? Around intake plumbing. intake to head gasket. do this while the engine is cold. before it gets hot. Have you removed the carb insulator recently or done intake work?