I should have known that it was running right as a fluke as I never really found anything wrong. It started surging again after about 10 minutes or so of running. Quite bad at times... almost stopped. So this morning I cleaned the carb again. This time I managed to remove the emulsion tube and it had a lot of what I can only describe as floating black bits of mold in it. Same as the little piece I found earlier under the middle welch plug. Same stuff that seems to be coating part of the bottom of the plastic gas tank. Anyway, I cleaned it out. Also removed the welch plug over the small tube that fits inside the emulsion tube. Couldn't get it out (actually scared I would break it trying), but forced a lot of carb cleaner down it and was vicious with the compressed air. All back together and I just finished using it for about 1.5 hours and it ran like new.