The key to mouth calling is huffing the air over the reeds instead of blowing it. Just like you are cleaning a pair of glasses. You then must learn to constrict the airflow over the call and use tongue pressure and a whole lot of other things to be able to produce the calls. You can learn how to do all this with time. It would take a lot of explaining here to perfect your calling.
It took me years to be able to compete with the best callers in the world and now I teach others how to do it.
Hopefully we (River Valley Game Calls)will have a dvd out shortly that will demonstrate what i am talking about. Until then keep practicing....