If the hsab is already as small as .025, you’re already very near the small end of what would be anything close to “normal”. The smallest Holley sells is .021” I believe.

It’s your car, but imo you’re making a mistake by not verifying the fuel pressure at wot.
It may not be the whole problem, but it could contribute to making it more difficult to solve.

I vote for the “known good carb” test.
This is strictly a test to see if another known carb also requires the jetting to be grossly upsized to cure a lean condition at wot.

There’s an old saying about Holley type carbs that holds true much of the time...... and it’s along the lines of...... “if you have to increase/decrease the jetting by more than 5 or 6 sizes from how it came ootb(to get the wot a/f ratio correct), it’s the wrong carb for the application”.
Extrapolating on that concept a bit......... you could also say the carb configuration is wrong for the application.

IMO, jets, air bleeds, emulsion........ are “tuning” items.
If you don’t have a fuel delivery problem, I don’t think your carb can be cured to the point where you have a good balance between part throttle and wot by “tuning”.
It’s going to require some parts be changed.

Assuming adequate fuel flow and pressure, an old school Holley 4781 would be plenty rich(probably too rich) on that motor with 84/84 jetting and pv’s in both ends.

The reason I asked about the valve springs is, if the valvetrain is experiencing some instability, it usually shows lean on a wideband.

this might be a thread on the same model carb.

looks like he might have .032 hsab, and also the old style metering blocks, so not a ton of emulsion...

https://www.tapatalk.com/groups/racingfuelsystems/pro-950-carb-good-base-line-t504.html

I just replaced the pump on my truck that I thought should be large enough to feed the engine (performer rpm mechanical). I found that fuel pressure was dropping to 4 psi at wot. Although the pump change alone did not help my et ( I think I have other issues), it does help to know for sure if you have the correct fuel pressure.

A worn fuel pump push rod will cause the problem. sorry if already mentioned.

The HSAB size is not the sole source of emulsion air, changing from a .025" to .021" has nothing like the area proportion (28% leaner) effect on A/F.

The point I seem to have been unsuccessfully trying to get across thus far is....... 84/84 jetting with pv’s on both ends is plenty of jet area for a properly configured 1.56x1.75 carb to supply enough fuel to a 500” motor that makes 550-600hp.
Especially if it’s got .025” hsab’s in it.

The jet area isn’t the real problem here.

I wonder what the driving situation is for the OP, what engine rpm and what the vacuum reading might be, this is going to be constant rpm I'm guessing.

Could this be a problem with the power valve?

could he be running 5000rpm on the highway for a few miles and have the vacuum high enough that the PV starts closing?
would the motor be able to run leaner at that speed if it's a light load 5000rpm cruise?

fast68 is definitely pointing out some variables that should be looked...
I would try a known working carb to on the car.

Yes, that is a possibility. The OP hasn't provided us with enough information to solve the problem. (which of course is the main issue on Moparts. But to be fair, if people knew enough information to help us solve their problem they could probably solve the problem themselves in the first place)

If it was my car I'd return the carb to stock and start my testing over again. If the car works just fine everywhere except for WOT then I'd suspect fuel delivery. A fuel pressure gauge would be the first thing to add. If there is plenty of fuel pressure but the engine still goes lean at WOT then I'd try to find the next choke point in the system. Could be a clogged filter, a kinked line, a blocked off power valve, etc. Lots and lots of variables.

In order to maintain say, 4500- 5000rpm with 2.76 gears(about 130mph @4500 with a 27” tire) i think would require a fairly substantial throttle opening(the OP should be able to answer that question).
Enough to where I doubt you’d be making enough vacuum to close the PV.
And if you did, you could just install one with a higher rating to make sure it stayed open.

However, the pvcr isn’t enough of an increase in jet area commensurate with the adding of 15 sizes of jet, like what the OP has done on the rear.
So, even with a PV plug installed, it shouldn’t need 99 jets for adequate fuel flow.

One thing I would try after I did the “known good carb" test would be trying larger needle and seats in the 950....... assuming the known good carb didn’t also require a massive jet change to get the a/f within a reasonable range.
If the known good carb shows it needing similarly upsized jetting...... I think it would be safe to say the problem isn’t the carb itself.

In air bleeds that's a HUGH change.........And the .021's are more of a "pre drilled" deal than most would run imo...........

I will say this that I had my 850 Holley DP jetted for the track and dialed in pretty good. But I felt it was a tad fat at part throttle when cruising and it is an older model as the only jets in are the main jets. Everything else has to be drilled and or tapped for jets. I was going to modify the idle restriction and transfer slot sizes but I decided to drop the primary jets a bit first and then open up my primary power valve channels some to make up for the less fuel at full throttle.

And I only had to drill just the P/V channels. I dropped my main primary jets a few sizes and opened up the P/V channels the same amount as I measured the sizes. And it has worked great as it cleaned up my part throttle very well and it seems to still pull as hard. But I have not been back to the track to verify my trap mph although the car feels as strong when wide open. I did not want to change it much because it was dialed in great at the track so I went with the simple jet change and drill the P/V channels first which has worked good for me. One thing I found is if a carb has been messed with and I don't know who has done what to it I like to go back to stock jetting and then work from that. Good luck with it. Ron

Just a little something to help put into perspective how much of a change the OP made to his carb jetting....... assuming you took out Holley jets, and replaced with Holley jets, going from an 84 jet(.098”) to a 99 jet(.126”) represents an increase in jet area of 65%.

On the primary side he is running 92 jets and a PV.
Assuming the current pvcr is around .060(this is a pure guess, it’s likely smaller), if you wanted to be able to get back to the 84 jets and still have the same jet area as a 92 jet(.110) and a .060 pvcr, you’d need to increase the pvcr to .093”.

I’m not advocating doing this, I’m just showing what it would theoretically take to do it.

FWIW My 1200 cfm Dommy has .082-.090's and has a nice linear fuel curve from about 11.9 at the hit and graduates to about 12.9-13.0 at 7000 rpm's and even Steve Brule at West tech dyoned two carbs of mine and was impressed with the curve. If you clean up the over emulsified carbs put out these days and size the high bleeds accordingly, you'd be surprised how little jet is needed............

I will say when I jetted down a tad on my primary main jets and drilled my P/V channels I measured my jets with my drill gauges and the P/V channels and did not care about the jet number as I dropped .003 in size on my main jets by size and not number and opened up the P/V channels the same amount. Course that's because the Holley jets are not always the size of the number on them mostly when you get into the mid 60's and up. Ron