[HSSS427]

I'm going through almost this exact scenario now. Had Holley 4150 - 9379 (no choke, mechanical secondaries, 750cfm, annular flow) replaced the main body with ProForm and also replaced the throttle plate with the ProForm unit as well.

Having a heck of a time getting it to idle. I came close and it would idle at about 1200 rpm. This was with the idle mixture screws on the primaries 2 1/4 turns out from the seat (vs the suggested 1 1/2), secondary mixture screws were 3/4 turn out, I had the idle speed / throttle stop screw turned almost all the way in, so probably exposing the transfer slot too much. However, I also have drilled small 3/32 size holes in the primary throttle plates. This main body also has a idle speed screw for the secondaries and I've now got that opened up some as well.

Base timing is at about 20 degrees and it certainly seems to like more advance in order to idle.

This is on a 427 side oiler with an Isky cam 250 duration .525 lift.

Not sure what to do at this point......
Thanks!
Scott