Sounds like retarded ign timing, any chance the distributor is loose, or it's internals loose? A loose distributor will slowly retard as time goes by causing power loss and higher temps. Blowing exhaust gas out the intake means the engine has rotated backwards. Not a big deal, just means it's having trouble with fuel or ignition, usually the latter has been my experience. I can't help with the idle screw, I messed with mine too, but I just had the luxury of adjusting it by feel on a normally running engine.