Power Valve Issue?

[pusherfans]

I have a drivability problem. I have used an O2 sensor to tune in my 4150HP Ultra (950 cfm) on my FE (bored and stroked to 527). The problem is at just touching the gas to keep speed at 1800-2500 rpm, it sounds and feels like a 2 cylinder John Deere tractor, but in the same rpm range giving it 1/4 thorttle or more, it sounds and drives fine, but also accelarates quickly out of that rpm range. I even bogged it down to 1200 rpm up hill in 5th and at that range with minimal throttle, it does that "flutter" but with 1/4 throttle, pulls right out. I am thhnking that this flutter is the power valve, because this is what I was told by the Holley guy on the tech line.

changes to carb are: power valves were changed to 8.5 (stock was 6.5). this is contrary to what I have been told of half the idle vacuum, although, I have not measured the vacuum, but I made this moved based on the mixture being perfect across the board, except at 3/4 throttle, where it was way lean. So it made sense that I wanted the power valve to open sooner. I was also told this by the Holley guy on the tech line. WOT was perfect mixutre, so changing jets would have made the car rish all the time. (perfect to my engine builder is 12.5-13.5 a/f). In that same area of just touching it, it was around 11 - 11.5, but was never affected by jet size or power valve change.

The cam is long duration, lots of overlap and 633 lift, so I assume it would have low vacuum at idle.

The interesting thing is that I did not notice this funny running when I first put in the 8.5 power valve, but then I was concentrating on 3/4 to WOT and was not just cruising.

I did keep finding little pieces of Holley blue gasket inside the bowl each time i opened it to change jets. I cleaned them out, but I suppose something in the metering block could also be clogged? I changed to a diffeent brand gasket and it no longer leaves bits behind. I will blow air though the passages and see if this does anything as well.

I ended up with jet size 75 all around. The carb came with 78.

So my question is: could this be something clogged in the metering blocks or the wrong power valve? If so how do I fix lean at 3/4 and good mixture at wot?