[Jack21]

Also have 700 Holley DP (#4778) on 351W.

Sounds like engine is running mostly on open secondaries, and you need to find out what is holding them open. The only thing that is supposed to be holding them open is that set screw. The only thing I can think of is binding in the throttle shaft, or the throttle blades in the bore. You may have to loosen the throttle blade screws and relieve any binding in the bore.

I have a hydraulic roller cam which pulls 15" - 16" vacuum at idle. To lean it out, I jetted the primaries back to 64. Set the primary throttle blades under the transfer slot, then set the idle speed with the secondaries. Replace the secondary set screw with an allen set screw (10-32), and you can now adjust it on the car with engine running.