Thanks CASO and Steve for the suggestions.
Comments/questions in no particular order:
1). The engine definitely seems to be running rich. But not sure if I can pin that on the carb when the choke plate is nearly closed anyway
2). The one aspect of the carb rebuild I wasn't quite satisfied with was the power piston. Despite cleaning it and it's bore, seemed not to move all that freely. But I had no context for how it should move, so I went with it. Could this explain my symptoms?
3). Exhaust flange bolts are seized up. Not sure what else to do besides sawzall the pipe. And I'm willing to do that if necessary.
4). Need to play with the heat riser thing. Any suggestion on freeing if it seems stuck? Hammer?
5). My thought for a quick and dirty timing adjustment. Move the ball to the lower (left) portion of window and get the rotor lined up with #1. That would be a few degrees advanced, no?
6). Should I do the dwell meter before playing with the timing?
