holley carb issue

Did you just stick it on and bust it off? You need to adjust float levels on any carburetor whether new, rebuilt, used, what have you. A used one in good shape may require float adjustment from one running engine to another.

The best thing to do would be to remove it, remove the float bowls, and adjust the floats with the bowls upside down. Looking into the upside down bowl, adjust the top of the float so it is parallel with the top of the float bowl. That is your baseline.