need help with holley 750 d.p

Like SG and JoeDust say, it's time to rebuild and replace the needles and seats. Floats could sunk/sticky too. When you rebuild, check for any rust in the carb too or it's just pissing in the wind if you have rust in your tank.

The only other thing to do is to adjust the float levels and that can be done externally on a Holley.