Holley 4150 dripping fuel from primary discharge nozzle?

Per your description, the fuel is leaking from the auxiliary venturi's which are fed by the main jets.
Possible causes:
- High fuel level but that sounds OK with the fuel just weeping out of the sight plugs while running (post #3). That usually eliminates float issues or high pressure or a leaking needle valve.
- Plugged air bleed(s); see post 11. Remove the metering block and squirt cleaner down from the top though the air bleeds and make sure cleaner squirts out in the holes near to top of the carb body where the block mounts. Then use that location to figure where the air bleeds go into the metering block and squirt cleaner into those holes; it should flow freely out of the main jets.
- Wrong/bad metering block gasket blocking the air bleed passaage from the carb body into the metering block. Inspect as part of the above procedure.
- Broken power valve diaphragm or bad gasket; inspect this. Perhaps just replace power valve.
- Too high an airflow at idle just activating the mains due to throttle plates not closing; see the above post and also check the primary throttle action with the throttle linkage disconnected for smooth action.
- Not being able to stall the engine with the driver's side idle mixture screw may be another symptom of the issue, or the driver's side problem is just worse (probalby is since it was easier to spot), or just may be that the screw's seat inside the base is fouled up. Remove that screw and shoot a bunch of cleaner in there and inspect for a burr or varnish or groove across the seat.