I increased the idle speed as well as enriched the mixture. Still the same. By the way, it only seems to happen after the motor is warm. Maybe the thermostat is stuck open, so the coolant would never get warm enough to adjust the butterfly in the carb to 'warm idle' setting? Would that make any sense? Thanks for your replies.
warmed up motor two seperate days and both times the choke plate was wide open when I pulled the aircleaner off. Third time, I watched it rotate to full open while motor warmed up. Seems to me that the auto choke is working as advertised. Any other ideas?