I have a MDS.78 that I could start alright but after a few tanks through it during breakin I tried to lean it out but I could not lean it out even after I turned the needle valve all the way in. I later read that the MDS had a proplem with their carbs, so I got a hold of Horizon Hobbies and I sent the carb back to them and they replaced it with the new C2 carb and now it runs fine. Give them a call. They seam to be willing to help guys out that have problems with one of these engines. Good luck!