Holley/Demon Carb stumble

With that venturi diameter, I think the Proform tune should be a safe place to start.

The QFT SQ-850, Holley Race Brawler 850, and Proform 850 all come with the same air bleed and jet package.
33/33 hsab, 76/84 jets.

It’s basically the same physical size as the original HP950, which is a much better carb for the application than a MD850....... imo.