Well I got back to work on the air leak on the 670 Champ the other day. I tried running saw and spraying around cylinder base, seals, and carb boot with starting fluid. Had no affect on it. I put new crank bearings and seals on this saw. Also a clean up of ports and opened up muffler. I was searching online and found an old post from AS where someone with a Champ had identical symptoms I had. He ended up finding the pulse line loose on the carb. Well my pulse line is in beautiful shape, but did fit a little loose too. I clipped off 1/4" and refitted line to carb. The problem seems to be solved! Saw runs amazing! It feels to have power similar to stock 372s I've run.
Long live the Champ!
I've said it many times, one of the best they made and one of if not my favorite saw.