On the one side of the carb you have a plate with a small hole in it. On Da50's it is usually to the side of the "bump" in that plate. The reason for the change in engine response during certain maneuvers is airflow within the cowl. This little hole senses air pressure both positive and negative and tells the carb to adjust accordingly.

The easist fix for this is to remove the cover, solder a small piece of brass tubing directly over the hole being careful not to allow anything to get into the hole and plug is or even worse have it tear a hole in the diaphram right below it once you replace the cover. Now replace the cover, attach a piece of fuel line to the brass tube and run it into the fuselage. This will help equalize the air pressure and it will stop the engine from changing settings in the air

Troybuilt models sells a nice CF plate for this and others have used a cut up soda can. It's important not to plug the little hole, just block air from directly hitting it.

Personal on the DA engines it's easier to use a cover than try to solder a tube over the hole do to the location of the hole. On most other engines that hole is right in the middle of the plate and it's a simple matter to do the soldering

http://www.troybuiltmodels.com/EngDesert.htm (about 1/3rd the way down the page. Look for "Carb Plate for all engines")

Also, head over to the gas engine forums and do a search, there has been a rash of discussions about this lately over there. Someone even went as far as building a nice little balsa box and running the end of the fuel tube into it to guarantee even pressure no matter what