Thanks Jim for the good information on dealing with airflow and cowls. I did not get to the field yesterday but did test run the engine at home... running it for a 6oz tank of fuel for 33 minutes continuous without problem. Noted however is that ambient temp was 56° rather than the 70° the day the problem manifest. So... maybe the problem is cured but warm weather testing is needed.
A couple of pics of the cowl.