All good info above but there is another possibility. A long time ago Someone asked me to look at a Holley that they rebuilt and had problem with the accelerator pump. Turned out the bowl gasket only had one hole for the accelerator pump passage and yes of coarse the gasket was backwards, perfectly blocking the passage.

Just remembered a brand new carb with a doa accelerator pump. The nozzle screw was pushing the check valve into it's seat. Screw was defective. Simple fix.