mine were fouling and after pulling the plug it looked like the electrod had been filed off at a 45 degree angle. I wenet through two sets of HKS same problem. I dont know why or what caused it (not detonation I ran with wideban 02 to check) but I switched to cooler NGK VX power and no problems so far? Also I now have a bad fule injector clip so dont know if that affected it but I dont see how?