well this is just a opinon but the first thing i would do is get rid of the exhaust throttle, to much work and time to get them right for no more than they do.....
as for the needle if you have a flow meter or no someone that does start it at 6 or so if i remember, not for sure.. every motor is different.....
what nitro are your running???
I can tell you from experience that 20 motors run best on 70% and higher...