On my engine - that is mostly stock except for the Demon jr and ignition set-up - the carb proved to be very sensitive to the primary float level. Raising it a 1/16 of an inch made an instant change. The Demon has such a large primary bore you are mostly going to tune the whole RPM range off the primary.
Do you have the idle transfer slot set-up as shown in the Demon literature? The primary throttle stop should hold the butterfly so that the exposed opening of the slots -seen from below - appears as a "square". When the carb is re-installed on the engine that screw shouldn't be moved - set the curb idle speed with the secondary. Takes a long allen driver down across behind the choke working from the front - rear throttle shaft stop screw is directly under the vacuum secondary pot. This whole operation took immense concentration on my part - to resist screwing in the primary stop to keep the engine running. Once I learned the secondary adjustment trick - things became more sensible.
I forgot to ask - my bird starts off in second gear as the Fordo autos all do - do you have a stick trans or an auto? Lots of tuning required to overcome the goofy second gear start believe me.....
Steve Metzger Tucson, Arizona