Hp 500's use staggered jetting and no secondary powervalve. 6.5 PV in the primary. A PV in the secondaries would be worth about 8-10 jet sizes.

Primaries port-81/starb-75
Secondaries port 89/starb-93

Carry a few fuel/water seperators with you for awhile, there may be $hit in the tank!

Sounds like the transition from the idle circuit to main circuit on the primary side is an issue...probably accelerator pump. Even if the carb is new...you can still have a cracked diaphram in the pump.

I would replace the pump...and of course the front bowl to metering block and block to body gaskets....you may have a leak there as well.

Last but not least...check the float level...should be even with the bottom of the bowl inspection plug just starting to dribble out. Believe it or not this has driven many good mechanics nuts until they find the culprit of the lean condition. Holley's are very sensitive to lean float settings.

Good Luck.

You are probably WAY rich running an HP500 carb on a stock 502

not a stock 502, but not built either, has a milder merc cam, and emi's