Hi guys,

I'm not too experienced in carbureted engines, I've only worked on newer motors. That said, I purchased a 1975 Firebird that had a GM Fast Burn 385 dropped into it in 2007. This is the motor:
GM Performance Engines | Fast Burn 385 Turn-Key | Chevy Crate Engine | GM Crate Motor | GM Crate Engine

So I have this problem where if I floor it quickly, the engine cuts out. The exhaust smells very rich, so I'm thinking maybe I'm running rich and the engine is drowning when I floor it. I looked up the carb part number and found an instruction manual on it, however I'm not finding how to adjust if you're running rich/lean. I looked straight down into the primaries and I can see the two jets of fuel when I open the throttle. There is a screw directly above the area where the two jets of fuel comes out that faces directly upwards, is this the adjustment for fuel/air ratio?
I'm aware that it might be something else causing the cut-out, but considering how rich is smells and the fact that i get 9.6 mpg, my gut tells me I'm running a bit rich.

Any and all advice is greatly appreciated.