Mine had a permeanet plug that I had to drill out, very easy to do,. I set it according to the jet kit instructions with the carb off but havent found a screwdriver small enough to set it while its in place and running.

 

The mixture screw is under a brass plug you have to drill out. It's on the bottom of the carb, engine side right in the middle. It should already have a small hole in it.
I put a 155 main in mine and it seems pretty good. I also left my lid on, so the 170 would be too big for me too.