I've gone through 2 plugs in less than 4 hours of riding recently. The arc short circuits from the center electrode to the side of the plug instead of across the gap. The symptom was that the bike would start but as soon as I opened the throttle, it smoke a lot and die. I could clean the plug with a wire brush and the bike would start and run again until I revved it. I put a new plug in there and everything is great. I don't know of the insulator is cracking or if it is carbon tracked. I'm running a NGK BR9EIX. The local shops are always out of the copper plugs and at $10 a pop for the iridiums, I don't want to be replacing these things too often.