I had surging issues with mine running an APC11X6. After cleaning carb, needle valve etc I still couldnt get it to haul like it was after running it in. To get semi decent performance from it Im now running an APC10x7 prop and tached it today for the first time. After starting and letting it idle for about a minute I went to full throttle and got 13400rpm, BUT after about 30 secs it came back to 12800-13000. Im NOT happy with mine at all really and am considering replacing the ring and running it in again to see if I can get better. Ill try the 11x6 back on it and tach that soon as well, before replacing the ring.