Second brand new Holley carb flooding?

The issue with the street avenger might not be related at all.

I tried two street avengers on my 340, a 670 and a 770, both brand new. I could never get them tuned correctly to get rid of a lean spot (and stumble) at the primary to secondary transition. They would work great everywhere else, but under hard acceleration the car would go lean long enough for the engine to stumble before the secondaries kicked in. That was indicated with an A/F gauge. I changed everything, secondary springs, pump shot nozzles and cams, even jet sizes. Street Avengers are vacuum secondary carbs though, and I was never able to get the secondaries to be fast enough. I could flood it with the pump shot using a fast pump cam and large nozzle, but since the street avengers only have a single accelerator pump that hurt driving it the rest of the time. When I changed the springs I could get it to bring in the secondaries too hard after the lean spot, but not get rid of it. And that also caused the secondaries to come in under higher load situations, like pulling a long grade.

I swapped to a 750 DP and solved the issue completely. But that was with my 340, which puts out around 400 hp, and a 4 speed. After some searching I found that there's more than a few folks with 4 speeds that had the same issue, but folks with automatics didn't. With the hot 340 and 4 speed the mechanical secondaries worked better and the second accelerator pump took care of the big fuel demand going into the secondaries without ruining the primary shot. Just needed a carb with more adjustability to match the engine.

AJ/FormS said

Well before you write Holley off, Pay attention to the guys here.

You say "started it after letting off the gas and the motor winding down. The gas is coming out of the front lil tube that sticks up." So I just gotta say; This sounds like fuel slosh to me.
Four-speed cars with plenty of compression, during compression braking at higher rpms can decelerate so hard that the fuel can slosh to the front of the bowl. When this happens the float can fall into the void, and more fuel comes in. Now the bowl has too much fuel in it. Then when you get back on it, the fuel moves to the back, and up the spout.
Now with an automatic, this is less likely to happen, but if you are manually downshifting, it still could.
This is not flooding. The engine may even continue to run pretty good, until the sloshed fuel spills into the carb throats,upon getting back on it.
So if you are driving like this, your bowls may need baffling and/or the float level changed for your style, or just quit doing that, or install a dashpot on the linkage so the butterflies cannot slam shut, or open the butterflies some.
If you are running a lot of idle timing,the butterflies may be too far closed, and that would contribute to the slosh idea. I mention this because from the description of the "bog" with the first carb,(and the possible faulty T-port sync) this seems very likely.
In all honesty and fairness to Holley, 3 faulty carbs in a row seems like incredibly bad luck.

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Totally agree. My 340 can engine brake hard enough that I can see the results of the fuel slosh on my A/F gauge, especially in 1st and 2nd gear. It doesn't usually cause any fuel spill or engine bog with just compression braking, but it does make a difference. And on that note, I only run 3.55 gears out back with 26" tall tires. A set of 3.91's would make the issue worse.

I've gotten on the brakes hard enough though that I've had to pedal the thing to keep it running though, and that was definitely fuel sloshing in the bowls. Disadvantages to having 13" rotors and soft tread compounds I guess.

Baffled float bowls? Ever done it A/J? I'm curious. Might come in handy during an autoX.