Carter BBD tuning issues

Now that we know it is a 76', then I believe the Instruction sheet suggests 2-3 turns of the air mixture screw counterclock wise as a static setting.(right fully closed, then 2-3 turns left) don't screw the mixture screw too tight, just snug,barely. The vacuum hose to the distributer should be disconnected, so the timing won't advance at Idle. I seem to remember that year not having vacuum at an Idle anyway.
Once timing is set, look for 550-650 Idle rpm. Check timing again, and again as you adjust the Idle/mixture screw. you turn it in 1/4 Increments left or right to get the best Idle, smell for richness,etc. Once you are satisfied, get somebody to put the car in gear with the brake on to adjust the rpm so it will still maintain idle in gear. a slight drop in rpm is normal. It is a lot easier to show you than explain, sorry. fast idle asjustment is primarily for maintaining rpm during warmup, no other time.