The Holley could have a warped body where the metering block goes. This warpage allows a vacuum leak, and sucks gas directly into a vacuum port. Remove the float chamber and metering block and check the face of the carb with a straightedge. If its warped, use a fine file and dress it flat.
The warpage is caused by overtightening the four long screws that hold the chambers on, tighten them gently and in rotation.
Also can be caused by the cork gaskets shrinking. The newer composite gaskets don't have this problem.