Is this a two needle carb or an air bleed type? A two needle carb will have a screw inside the throttle arm (not just a screw that holds the arm on).

If it's a two needle carb I'd try setting it about two and a half tunrs out from fully closed, then turn it in from there until it idles well. (It should be pretty rich at 2 1/2 out.) Turning it in will lean the low end.

If it's an air bleed type there will be a tiny hole in the front of the carb and a screw to the side. Turning the screw will close off or open that hole. I'd start with the hole about half open. Just remember, turning an air blled screw in "richens" the engine because you're adjusting the amount of air, rather than fuel.

Hopefully, someone with instructions for the 25 PRO will be able to tell you definitely though.
Dennis-