I'm having problems with my carb leaning out at around 2500rpm with partial throttle. I've heard two different ways of fixing it. One is just a bigger PV and the other is bigger PV and increase my rear jetting. My current PV is a 5.5 and jets are 74/74. I had the jetting set my a dyno tune. The A/F mixture looks good throughout the rpm range, especially up high however just around 2000-3000 it's real lean and stumbles. It clears up once I get past that. If I go WOT off the line it runs fine, just when I take off normally and get on it about half way or so.

 

is this a holley 750 DP? do you have a pv on the secondaries? mine is jetted 72 prim. 78sec, no sec pv. make sure the transfer slots and air bleeds are clean.

 

If its lean at part throttle, I'd fatten up the primaries 1-2 jets and lean out the secondaries maybe 1 size. This will give you a similar mixture for WOT. Part throttle is all about the primaries, the secondaries won't even be open.
Another thing you might want to check is your ignition timing. At 2500 rpm most mechanical advance is in, and at part throttle vaccuum advance will also be in. Its easy to get into over 40 degrees of timing and if you have higher compression and not enough octane you could get detonation that kinda sounds like a lean spot.

 

This is a 650 QuickFuel DP. There is no PV is the secondary, the transfer slots and air bleeds are clean. The timing is set at 35. It's all in by 2500 or so. Anything more and it loses power on the dyno.