A 4780 holley 800cfm, came with 71p, 85 secondary.

seems like alot of jet you have for those carbs. I bet its really fat

My quick fuel M-800's came with 78/86 ... They also came with standard 6.5 pv's .. wonder why you have the 3.5? Seems like a big jump in power valve for such a mild cam.

one of the biggest misconceptions in the carburetor discussions, is that power valve opening point, can have an effect on idle mixture. The ONLY way a power valve can make a rich mixture, is if it were blown/ruptured, where engine vacuum will pull fuel thru the diaphram. When a power valve opens, it enriches the main circuit, which is inactive at idle. The idle circuit is what is active at idle.

For reference, On my 32 AT, I spin 24 Bravo's to 5100rpms with 502mpis with CMI's (425ish hp) and 1.36 Bravo drives on ext boxes for 72-73 mph.

That diagnosis would only mean the power valve that was in it was blown or leaking, I don't really think you can "blow" a power valve very easily on these newer carbs. Check your idle vacuum again, you may need a different power valve... and jet accordingly.

once upon a time they sold kits to prevent power valve blowouts (usually due to a backfire). Then some of Holleys competitors started including power valve protection standard. I have know idea what the current situation is.

They still have them. I believe the became standard after '92
https://www.holley.com/products/fuel.../parts/125-500