Yes, in the parts breakdown for your carb....the Main Mixture Screw (part no.34) is NOT listed. See the enclosed link...page 138.....your carb listed on the end of the column...far right.
http://www.lawnmowerpros.com/PDFs/Za...PARTS_LIST.pdf
This is an excellent parts diagram breakdown and better than the one on the Zama site as it is clearer...and all the models and their respective componets are listed, but unfortunately the RB-K66B does NOT have the main mixture screw.