So it runs amazing but it runs poorly.
Maybe less time spent listening to crackheads.
Uh...yeah, what dot?
This is…meaningless. For one thing, that screw you're thinking of adjusts only the idle mixture. For another, adjusting it isn't a matter of a specific number of turns, but even if it were, 3-1/4 is more than they usually wind up at, suggesting something's wrong.
Making a dual carb setup work well is highly dependent on both carbs being identical (not just "two Carter BBSs"; there were many, many different BBSs with significantly different calibrations over a buncha years). And the carbs have to be in functionally flawless condition, which is difficult even just one-carb-at-a-time, let alone two.
And there's a lot more to tuning the engine than pointing a timing light and going "yup that's on the dot".
And shorty headers aren't usually a top pic for a street-driven Slant-6.
And there's no info on the rest of the car. How many miles on the engine? What's the exhaust system configuration? What transmission, what rear axle ratio, what tire size?
It kinda sounds like you tossed some nifty-sounding/looking parts at an otherwise-stock car and expected a big boost in zoom. That really isn't howw it works.
