I didn't know about the venturi issues.
I have had two 600 edelbrocks with that stumble!!!
My 800 was as smooth as butter, ran harder than the 800 holley-that I didn't spend much time on tuning.

I have always been able to tune any stumble out of a Carter or Edelbrock.
You do have the check ball/ needle under the squirter, and if it's a needle it is in the correct direction, and there is no trash under the needle, right? Dave

I was able to tune around the stumble too, by giving it a lot of mid range fuel. This hurt mileage to the point of hating it. Both of those trucks are now sold.
I often thought it was just wrong passage sizes in the off idle circuit.