Tom,
We had a 825 Demon on our sbc car before we put the injector on. When we had it on the dyno we could not get the a/f right at the upper rpm range. We were getting a lean condition. What we found was the needle and seats that came in the carb, although they measured .150, would not flow as good as a set of .150s we had in our old Holley that we tested against it. We changed needles from the Holley and HP went from 690 to 727. Not sure if it could be the same problem but we have dyno sheets that proved it for us with that being the only change.
I will say that once we tuned that Demon it was a great carburator. When we changed to a toilet every one was telling us we would pick up a few tenths. We didn't pick up anything at all. Not that this helps you any just saying I think Demons are pretty good carbs, like most things, when they are tuned right.
Curtis