The early Demon carbs were notoriously hard to tune. They were missing an adjustment (Idle Eze) that was added after Barry Grant started getting complaints. Some changes were made in the Demon carbs, which made them perform better, but by then, the damage was done, and Grant filed bankruptcy. I finally dumped my street demon and installed a Holley Street Dominator.

I know those Demons CAN be tuned, and they CAN run great. Mine just wore me out.

Link to an article on the Idle Eze