I used this article as a guide:
http://www.geistware.com/rcmodeling/...ine_tune_1.htm
and my engine is doing much better. I set the needle valve lever a tiny bit lower. This has made the idle more consistent. On the other hand, the engine is a little harder to start when cold and top end turned slightly leaner (I had to compensate by opening the high needle a little). I am going to keep it like this for now since I have other issues like end play that may require more extensive repairs, if it's worth it.