How's the secondary ignition system (plugs, wires, rotor, cap)?? Timing? Total advance checked and functional?

Once proven, it could be time for a rebuild kit, starting with new needle/seat assemblies, a power valve and cleaning out of the metering block passages.

If it's "pig rich", Holley's are known for weeping needle/seat inlets and blown power valves.

Check for a vacuum leak too.