Inconsistent idling problem

As for the fast idle change, do you push the pedal to the floor once before starting cold? You have to do this to kick on the choke and fast idle when starting. (Some guys who grew up on fuel injected cars don't know to do this.)

Also, does this have an electric choke? You may need to adjust the choke setting to get the fast idle to consistently come on. And you should be able to manually manipulate the choke linkage to the stepped idle cam to get the idle adjustment up on the fast idle cam step(s) at any time, to check the fast idle RPM setting.

As for the variations in idle speed, take the carb off and check to see where the primary throttle plates are setting at normal idle. They should be open a tiny bit and the edges of the plates should not resting against the throats. If not, then then secondary plates may not be open the right amount, and the primaries are being closed to rest against the throat, which is wrong. This will cause inconsistent idling.