Demon is a good carb.
Power valve blocked in the rear is good for street/strip. If you were road race you could install PV in the rear and square jet the carb.
1st thing I would do is get more intial timing 24-26* 34 total mechanical.
Next is check what you have. Previous owner may have changed original settings. Demon jets run bigger than holley. Use one or the other when changing jets. Ex 79 Demon is = to an 80 holley.
72/78 jets are more in line with a demon 650
71/79 is stock jet for 650
My guess is you have a 650. A 750 with 72/78 jets would be lean.
http://documents.holley.com/lit705rev.pdf
Check the airbleed sizes IAB .070 MAB .039
I run 75 PMJ 84 RMJ
Set float to lower line on site glass.
My regulator set to 6.5 psi
