Ok, let me preface this post by admitting my ignorance regarding Q-jets.
Schurkey, I read a response you posted on another topic, "Qjet Idle", suggesting a missing hot idle compensator as the culprit for a poorly idling Q-jet. Could this be the simple fix to my months long carb problems? I have the provision on the back of my 68 Q-jet #7028211 for said compensator, but alas, no compensator is installed. Did all q-jets of this vintage have the compensator or is the provision for one simply part of the body casting? How do I tell if the compensator should actually be there?
Any help from anyone is greatly appreciated...
Patrick

if it has a little cover screwed on to the boss for the HIC, it probably needs it in there.

Use a mirror, look at the back of the carb, look right straight into the boss. pull the cover first if it's there. If the boss/cavity is empty, look to see if there's a hole drilled into the bottom of it. If there is you need to get the HIC or permantly plug the hole. You probably don't actually need the HIC, but oyu can't have a big vacuum leak either.

Alright, looked with a mirror at rear of carb. At the base of the cavity, there is a horizontal hole, but it does not go through the valve body. Should I be looking for a vertical hole?

start it up and put your finger over the cavity. if there's a vacuum leak you'll find out about it.

What he said. Most carbs have the bosses for the holes, but they have not drilled them through the casting to make 'em functional.

If it's drilled through, it'll suck air like crazy.