Not trying to be argumentative with anyone here, just some observations on Demon carbs that I've had since I work for a speed shop which has been selling these carbs for a couple of years:
-literally every customer that I have sold a Demon to has had problems with an off idle stumble that has proven to be difficult at best to tune, even with the help of B/G technicians
-many Demon carbs seem to have very unresponsive idle circuit tuning
-at least 30-40% of the carbs I have sold have had metal particles in them that appear to be left over from machining processes
-several have had loose power valves right out of the box
-A reputable local performance oriented tuning facility that is equipped with a chassis dyno has repeatedly reported that the fuel curves of various Demon carbs they've tried to tune are all over the place, and have in almost every case replaced the Demon carbs with Holley HP carbs, which have consistently shown stable fuel curves along with horsepower and torque increases on every vehicle they have switched over.
-A reputable local engine builder who offers many high horsepower turn key engines had a customer's 500 h.p. pump gas small blah Chevy on the dyno. The engine was equipped with a 750 cfm Speed Demon with mechanical secondaries. After optimizing the tune on the Demon for max power production, they then installed a Holley 750 double pumper (#0-4779) with choke and all just for comparison. In out of the box tune on the Holley, the engine picked up 17 horsepower at peak on the very next pull, and the gain was repeated on the second pull with the Holley. The Demon was reinstalled, and horsepower promptly dropped.
Personally, I am not impressed with these carburetors. There are some very nice ideas behind the Demon line of carburetors, but I think the execution of the final product is poor, especially for the money the customer has to spend on one of these. For those that have had success with them, great, but I myself will stick with Holley. Just as FYI, the thread size in Demon float bowls is 9/16"-24 (same as a Holley 1850). Just about all of the major AN fitting suppliers have fittings that will work in these bowls.
"My car would be fast if it had an engine, transmission, and rear axle in it."