Right below the threading, and under the AFC ring, is a groove. If you take an o-ring from a kayfun tank and put it in that groove (takes a little massaging to get flush) the AFC will no longer spin freely. That simple fix made the Magma go from "good" to "great" for me.
Also, not my idea. I read it somewhere.
Do you know what size this o ring is? I don't have a kayfun. I have a few o rings in my stuff that might work just wondering if anyone knows the size. My Magma is on the slow boat right now.