Not at all uncommon with those carbs.
BG had a really good dealer program, where a small shop could sell a carb and match Summit or Jegs on price, and still make a decent profit on them.
But, not one of them ever came ootb and ran great with only an idle mixture screw tweak.
We’d waste a bunch of time sorting them out on the dyno.
Eventually we just stopped selling them, since an equivalent Holley was so much less trouble to get dialed in …….. and have the customer happy.
Several of the Demon units we got in were real horror shows.