A couple things could be happening. You're adjusting the water level too high (at the time of adjustment it probably looks ok), but as the foam head builds, the water level also comes up some, and bam, you overflow. Set the skimmer in exactly 9" of water, and adjust the actual water level inside the skimmer to where it's right inbetween the collar and the bottom of the collection cup. Then let it go for at least 48hrs before making anymore adjustments. If this is still causing it to overflow, then make 1/16th of a turn open on the wedge pipe, and let it set for at least 2hrs before making another 1/16th turn if need be.
If the wedge pipe is wide open and the skimmer still overflows then it's setting too deep in the sump, or the skimmer is reacting with something in the system that is causing it to overflow.