Get a strip tuning kit and read the little book that comes with it and grab a vacuum gage. My impression is the step up spring is probably too heavy, and the jet/rod combo is too rich.
For some reason that manual I got with it was for a performer carb. I will see if I can download. I think I will start with pressure reg as think a stock mech pump puts out closer to 8 or 9 psi.
