Rommel, I tried the 750 speed demon. It idled but, not as well as the E-brock 750. I also lost bottom end, but seemed to gain some at higher rpm. I didn't experiment with the jets, yet. Also, had a bit of trouble with the throttle linkage and cable. The pedal is VERY high with the Demon carb. I put the E-brock back on.
I'm a hobbyist. Not a professional. Don't be hatin'!