Hey dorfs again!
Firstly, thanks to xyj173 for the suggestion. All air cleaner related attachments have been checked and are operating properly, except for the faulty air injection tube.
Now dorfs - curb idle and fast idle have been set to specs. I tested the pull off by disconnecting the hose and after gently pushing the diaphram to it's seat with my finger, I placed another finger over its vac inlet hole. The acid test here is if the diaphram holds, then it is still in working order, which it is.
Now - with the engine cold in the morning, I took the air cleaner off and watched the choke plate. I hit the throttle once and the plate closed as designed. The idle screw was on the second step of the cam. I then started the engine and immediately the pull-off went to work and backed the plate off to specs as designed. Then the "event" began again. The engine began struggling, almost as if smothering itself. I tried moving the plate to see what would happen, but that didn't help. Then it killed as I knew it would. It seems reasonable that if the check valve on the exhaust side is not working, that exhaust gas would back up into the carb, but I can place my finger over the hole and there is almost no movement of air at all. But I'll replace that right away anyway. I might get lucky. -- Wait a minute, it just occurred to me that the problem still occurred, even with the air cleaner off, hence, the air injection tubes were not in contact with the carb, and not subjecting the carb to exhaust gas. What now?
By the way, you mentioned my Oxy sensor forcing the carb rich, but I did the Nutter computer by-pass last week, so it should be having no effect on the rich/lean mix, right? Also, even though I don't want to polute the air, emission inspections have not made it to Louisiana yet. The stupid emissions system is what's causing my pipes to billow black smoke in the first place.