Street Demon or Edelbrock AVS2 or ?

Not sure what 'way out of it's comfort zone' means [ Post #48 ]. Or that the secondary AV spring is 'pretty fragile'.
If this 800 cfm carb is out of it's comfort zone, it might be too big for the engine & a 625 cfm version might have been better.
Lean spot on sec opening can be a few things: float level, jets too small, spring too loose. And that is just the carb, not talking about ign etc....