I have been trying to teach myself how to do flutter tonguing. I think I understand the technique and I can kind of do it sometimes when I don`t have a clarinet in my mouth. The trouble is that when I put a clarinet in my mouth I can`t do the technique.
Does anyone have any advice for this problem?
I`ve had problems in the past with tonguing, and also with my embouchure being too tight and restricting movement. Could this be behind it?

That`s the exact same problem I had- my embochure was way too tight, what I did was just loosen up my mouth as much as I could, and it worked right away.