Holley Street Avenger on 408 / 416

I don't think the street avengers are bad carbs at all. One thing to look out for on them is how the lever arm contacts the pump cam, some of them need some adjustment as they can be a little loose from the factory, which can lead to a lean spot on acceleration because there's a small delay on the accelerator pump shot. Doesn't seem like that's a big issue from the video. With my wideband I was able to get both the primaries and secondaries tuned in great. I was just never able to get the transition between the two quite right, and I tried every secondary spring, pump cam, and nozzle I could think of. But, after talking to a few people it seems like the issue on my car was the vacuum secondaries. With the engine I have, and the 4 speed, the mechanical secondaries are really the trick. I think that if I had an auto in my car it wouldn't have been a problem. And on that note, when my GT gets back on the road it will have the 670 on it. But its a little milder as far as build goes, and will keep the auto trans.

Back at the original OP, is that your car in the video? Seems to me like its dumping too much fuel for the amount of throttle you're giving it. The secondaries aren't even opening because its a no-load condition there at idle, so its all on the pump cam and nozzles. An 870 has a #40 nozzle, the 770 has a #25. That's a BIG difference. I never went any bigger than a 35 on mine when I was tuning the 770 (it was overly rich at that point). You have more cubes, but your 408 doesn't sound as high strung as my 340 (which is actually 350 cubes @ .060") .

Also, what is your vacuum at idle? The 870 also comes with a 4.5 power valve, which may be too low if you're pulling decent vacuum at idle.