What happens when you continue at WOT? Does the AFR lean out again?
If it does, then, it's not the jets and you need to focus on the accelerator pump nozzle or pump cam, vacuum secondary springs, and power valve. If the AFR stays at 10 even after you've held WOT long enough for everything to reach steady state (ie, secondaries wide open and accelerator pump shot gone) then you need to look at the jet size.
Keep in mind that with a street avenger you only have one accelerator pump, and it's on the primary side (not like a double pumper which has one on the secondary side too, hence the name!). So, you can make the pump shot smaller, but that will effect the AFR's even when you're only on the primary side. Meaning that you'll also lean things out even when you're just doing part throttle acceleration. If your AFR's are great except when you go to WOT and kick into the secondaries then you probably want to leave the pump shot alone and concentrate on the secondary spring, power valve, and secondary jets.
Another trick to check the power valve is to accelerate up a long grade. If the power valve is coming in too early, you'll see it while pulling the hill under load. Obviously you don't want to run lean doing this either, but on a long grade you can judge how soon you want the power valve to come in, using your acceleration and AFR to judge when it should be kicking in. If you work the pedal right you can pretty much look at just the power valve, ie, with nice steady acceleration you can mostly keep the accelerator pump and secondaries out of the equation as long as you don't accelerate too hard. That will show you exactly when the power valve opens up, and you can decide if you want it to be later or not.
I had the opposite issue with the street avengers on my 340. I tried both 670 and 770 avengers on my Duster, and I could never get rid of a lean spot when I stomped on it and still have it run decent the rest of the time. I adjusted the pump cam, pump nozzle, power valve, secondary spring, secondary jets, even primary jets trying to ease the transition some. If it was right on the primary and secondary sides at "steady state" it was lean in the transition, and if the transition was close it was drowning the car in fuel on the primary side. I had to go to a 750 DP. But I've got a fairly hot 340, it idles around 9" of vacuum, has ported heads, 9.8:1 compression etc. And a 4 speed. After a lot of research I've come to the conclusion that the vacuum secondary carbs have a hard time keeping up with a 4 speed, especially with hotter engines. The mechanical secondary DP dumps fuel at the transition to WOT, which is apparently what my engine needs. With an automatic transmission things work better for the vacuum secondary carbs, just has to do with how the transmission loads the engine I guess.
