I am having trouble with my DA50 richening up a great deal when it is in the air and I believe that it is because of an airflow problem in the cowl. The engine is mounted on an extended firewall box with the back of the carb being about 1/4 of an inch forward of the firewall. I think I might have two problems. The carb mixture diaphram plate originally had the vent hole mounted facing foward. I turned this around so that the vent hole now faces backwards towards the firewall but that didn't help. Still very rich in the air. I might try to modify the cover plate by putting a new hole in the center of the plate and running some fuel tubing into the fuse. My other possible problem is airflow into the carb. The hole in the firewall behind the carb intake opening was drilled only just a little larger than the carb intake size. Should this hole be larger and could that cause the mixture to richen up when in the air?