Weber does have basic rules also for weber carb adjusting. So many turns out, So many turns in and if it doesn't fall within this specification then you make jetting adjustments accordingly. In our manuals section of this forum, there is a weber manual dealing specifically with the weber. This may help you also. Depending on your elevation also can determine requirements in jetting.
I would do a basic check on how many turns that mixture screw is out and start there. The 170 seems a little off to me since I think I use about a 165 with headers, short dump exhaust, ported head and a race cam @ 2000 foot elevation, which elevation doesn't make a huge change, but it has some effects.