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Message: [QUOTE="spanky250, post: 153149, member: 20897"] If the tip of the plug was melted awat, it was either very lean, or detonating badly for some reason, possibly both, the pinging could have been caused by lean jetting. The short wamr up time you described can certainly seize a piston, new or not, and it's much more likely with a new piston, especially a forged one, but that would not melt the plug. After repairing it, I would jet much richer before riding it again, and jet it a step at a time after break-in ( which needs to be more than one short warm up). Why did you rejet anyway? Did it run rich or lean before? How much did you change the jetting? If your engine is basically stock other than the exhaust, you shouldn't have to change it very much, and my experiece with aftermarket pipes is they require you to make the main one or two sizes richer, not leaner. I'm sure some bikes are the opposite, but none that I have owned. I have to disagree. the running time is not the issue, it is heating-cooling cycles that a new piston needs to relieve the trapped stresses in the metal from the manufacturing process. Without this, it is just a guess if it will run or blow. If it is a forged piston with tight tolerances, it will most certainly seize this way. [/QUOTE]