Well, it seems to behave the same with the cowl on as it does with the cowl off. And as mentioned it ran fine on the first tank of gas and for 10 minutes in the air. There was a specific point when something changed in flight that caused the problem. I would think if it were a turbulence problem it would have been present from the beginning. P.S. I just took a look at your BME 44 on your web site. It's the same motor and prop I'm running, but I have to run the stock BME muffler.