I have a new OS 160 with ~ 1 gallon of fuel thru it, which is having a fuel delivery problem, the motor cuts out when angled sharply upward. We have replaced and or inspected all fueling hardware, etc. , except for the carb oring. I am using a Pitts muffler, and was told I needed some back pressure, so I have nearly blocked one of the pipes, but still have the problem. I am tired of dead stick landings, any idea? ben