74 Dart possessed by Satan...

Set the curb idle screw first before the fast idle. Do you have a tach or a vacuum gauge? With the car warmed up, timing set correctly, crank the idle mixture screw in til either you see a drop in rpms or vacuum, then slowly go out again til you get the best vacuum reading or the highest rpm reading with the leanest mix. Cranking in leans out the mixture, cranking out fattens it. Then adjust the curb idle screw for the correct curb idle.
For the fast idle screw, with the engine running, set the fast idle screw on the 2nd highest step of the fast idle cam and then adjust it in or out til it reads the desired rpm. Kicking down the throttle should release the fast idle can and the rpm should return to the curb idle you set before. It it does not, look for a bad vacuum diaphragm or something hanging up in the choke linkage or a bad choke coil.