car147,
I had the same problem with my DA and here is the way I solved it. The pop noise in my case was the engine going rich in the air because pressure builds up in the cowl as the speed of the plane increases. As many others the engine was fine in the ground.
The solution was to solder a brass tube in the carb diaphragm hole and put a tygon hose on it. Then I though that if the pressure was building up in the cowl it should be also building up in the fuse so instead or routing the tygon line into the fuse or to the balsa box (what a pain) I just took the line outside the plane in a place where it was not subject to direct airflow (In the area where the landing gear is mounted on the plane). Outside the plane the pressure is the same and if you don´t have any airflow induced pressure you will be fine.
The result is that my engine runs perfect not matter if the plane is inverted, knife edge or whatever .
Here are some pictures
[img][/img]
I think the carb in this engine is very sensitive to pressure changes.
Hope this helps,
Andres