Thomas B,
I would take the S/G off and check the brushes. They may be worn down and need replacing. My 149 would start fine but then charge sporadically with the ammeter needle jumping wildly from zero to high charge back and forth. When the brushes get worn down, they can hang up on the brushholder and not make good contact for charging. New brushes took care of the problem. Also check your S/G bearing(s) and/or relube the oil wick in the end cap bushing if you have the later style S/G while you have it apart.
I also had to repolarize S/G after changing the brushes. Some here on the forum say you don't have to do this since the S/G gets repolarized when you start the engine but I had to do it to get my S/G to charge properly, otherwise it would just barely register a slight charge. After repolorizing, it has run like a champ ever since. Hope this helps.