More carb tuning problems.

[JAM1775]

I differ with some of the opinions especially that involving timing change or even to the long end changing the entire curve. . Since all you changed has to do with the air fuel charge you should be able to get your motor running crisp after ensuring your timing is exactly where it was before. Of course, once you iron out the kinks the better heads might like a degree or two of less timing on the dyno for that extra 6-8-10rwhp.

I still think 73F/78R is small jetting for your 392 and although you may get a crisper thottle response from the 650 you can tune the 750. For all we know your 750 may have larger than normal annular booster which would enhance fuel signal snap. I run a 11:1 351W with a roller cam at .576 lift , 750DP custom built. The throttle anywhere above 2800rpm is neck snapping , it idles steady even when at 130 degrees heating up and never stumbles on deccel.
As Holley would explain the nomrla spread in arounf8. therefore, I'd see no problem bumping up your rear jets to 81R....I think you'll see it rise up and roar at top end.

I'd want to get back where you were with this carb and this distributor where they are. Can you try bring all four corners out one turn and trying the idle screw for adjustment ? 1/2 turn on the rears seems too lean. The holes in your plates are okay, they let air in even when your plate is almost or completely closed. Yes...they can lean you out BUT you had it purring before with less motor ! Another trick is easy. Call the Holley tech line for direction first. the number is on their website. But.....you have 8 air bleeds which look like little jets all around your carb body. do not touch the 4 insides as they are for top end. You should not mess with those w/o and AF reading on a dyno. But...the 4 outer air bleeds are for idling. They can easily be removed . Go 2 sizes larger all around and you let MORE air in at idle. these air bleeds bypass the normal fuel pulling circuit thru the main body. By go larger you will intro more air at idle "under" the throttle body , leaning out the idle mixture allowing you to turn out your 4 corner screws adding fuel that way while allowing have more fine tune capability with the 4 corner screws. These 4 outside idle Air Bleeds do not effect by front or rear main jetting. They do however effect idle air/fuel mix and slighty lesser as rpm climbs near 2K.

But first ? Verify timing, PUT A VACUUM GAUGE ON YOUR MOTOR.
See where you you pull vac at idle , bring out your 4 corners to one turn each. Try to start and use the idle screw to get close to best idle.
Using tach and vac gaugeught to get you where you fatten or lean out until you see your highest vac pull, using the tach to keep your rpm near where you want it. 4 corner adjustments should be doen at 1/16th to 1/8 turn increments all around, rev the throttle , let it settle and examine the results. If you're going 1/2 turn you're going too fast ! Good luck and I hope one of us gets you to settle that bad boy down !