Just put the engine back in my cat after a couple of upgrades. 565CI/420blower/ Ken Jones 830CFM carbs. Freshened it up, installed a MSD crank trigger and daytona igniyion. Had it out saturday and all was good for the first 3 hours, never saw over about 4K rpm and 3# of boost. AFR's were around 14 at idle and 12-1 while running. All of a sudden it coughed and hiccupped once and went lean. 20-1 at idle, 14-1 running. Fuel pressure is 7.5# at the fuel rail. I have a large spin on filter right before the carbs. All 4 bowls are fuel of fuel, float levels checked, all 4 squirters working. I removed all 4 bowls and metering blocks, all are squeeky clean. I was doing all of this on the water, so resources were limited, but I see nothing wrong. Is it possible that a power valve can just stop opening and cause this? These have boost referenced power valves on the primaries, not that it really matters. I guess another option could be a huge vacuum leak, but I can't find one. The hoses to the carbs, MAP sensor and boost guage are all connected. I guess it could have blown an intake gasket, but I really don't think so. I used the good Felpro gasket with the silicone inpregnated on it, and again, never over about 3# of boost although I was about to let her rip, I hadn't yet. Any ideas?

Just a stray guess, but, have you checked the vacuum port on the base of the carb. I believe it originally connected to the choke.
Hope you find a simple solution. How did it run otherwise?
Good luck.
PS, I am not a Holley expert.

yes, all vacuum ports are still capped. The more that I think about it, the more that I think it must have blown an intake gasket.

Other than that, It ran better than expected. Idles at 800rpm, 600 in gear, no blower surge. The combination of the Daytona Sensors ignition with a crank trigger is the ****z on a carb blower motor. It even got on plane just fine with 1.36 gears and a 30" prop.

where are you getting the vacuum for the boost referencing?

right off of the back of the intake manifold

Boost guage, map sensor and power valve lines are all T'd in at the same place. I wonder if I can introduce a little propane into the crankcase and listen for the engine to pick up or watch the AFR guage and either verify or rule out the intake gaskets. I currently have around 8" of vacuum at idle.

that is how i do it.did you put a smear cote of sealer around the ports on the gasket?i don,t rely on the print o seal on the intake gaskets because i have seen them leak.

I only put a little sealer around the water ports, not the intake ports

Most carb issues I fix are lean issues from blockage.98% of the blockage's I never see. Using the red straw with your carb clean in both directions of every circuit and then using a rubber tipped blow gun from yourcompressor both directions has removed any non visual blockage I'n run into other than mouse pee eroding the aluminum enough to shut some air bleeds and small pieces of fuel line rubber lodged in frt of or in the needle and seat,

i too use propane to look for vacuum leaks. Unfortunately alot of vacuum lines and plugs immediately disintegrate with carb clean now.