Street Demon or Edelbrock AVS2 or ?

I have fitted two SD carbs, a 600 a 750. The 600 worked well, the 750 always had a flat spot. Owner rang Holley from Oz, unable to fix. All the usual things tried, bigger jets, air valve etc. He put his QJ back on, problem fixed.
I would never use one, they are poorly made & a cheap copy of the TQ.