I would not adjust the mixture until you first eliminate some other things

Replace air cleaner

Inspect and possibly replace spark plug

Check ignition timing and points (if any)

Is this an auto choke? If so, is there any sign of binding/sticking? Adjust it per factory specs

Best of luck.

The carb is non adjustable, but even with that, they tend to run lean because of EPA.
It sounds more like the needle & seat may be slowly leaking in the carb, if it's gravity fed from the tank.
You may want to smell the oil for the presence of gasoline. THAT would indicate a leaking carb.

Do check the air filter, choke & plugs

There was a message on this problem just recently. The usually cause of this problem is a dirty air filter. New after market air filters also cause the problem.