750cfm should be fine bro. I'm thinking like you are, that the intake is getting flooded, and can't get rid of the air/fuel charge fast enough.
Like Dark said though, check all the stupid stuff again. Float levels, vacuum hoses, etc etc. One time we went from a single plane intake, back to a dual plane. Couldn't figure out why the car was OBSCENELY lean. Had the biggest jets we owned in it, still lean. Then we remembered to re-check the float level. Swithing intakes changed the angle of the carb, and the back float was waaaaaaay too low.
The Devil's in the details, bites my butt alot too!
