Thanks for the reply(ies) to the questions. I have more:
1. If I can just plug the A.I.R. ports, can I just leave the ports on the air cleaner permanently plugged with the tubes disconnected and open to the engine compartment and not replace the valves? If not, why not?
2. I did all the adjustments on the choke linkages (except the choke unloader) after my problems began, but it had no effect.
3. My choke pull-off (vacuum diaphram) is functioning properly.
I'll adjust the choke unloader to rule that out too.
As I said in the post, she starts up immediately, but just won't keep running unless I can find that exact spot with the accelerator to keep it alive, and until it warms up, it chugs and spits soot and black smoke out the exhaust. I'm the type that wants to work on something until it is right, instead of abandoning the task. Kind of an anal-retentive thing. I'm also low on cash, so I don't want to go to the Weber yet, but this is discouraging.