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I have a 2002 Arctic Cat ZR 500, Last season I burnt a piston and the whole cylinder was replaced by a dealer. This year after about 800 miles, I burnt another piston, when i took the plugs out the left cylinder(The one which was replaced) the gap on the plug was completely gone. The end was pinched shut. Does anyone know what could cause this and if it was the cause for the piston burning up? Thanks for any help!
 

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Your main jets are either too small or dirty, causing the sled to run lean and burn the piston. What closed the gap was probably broken parts of the piston hitting the plug and closing the gap.
 

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Your main jets are either too small or dirty, causing the sled to run lean and burn the piston. What closed the gap was probably broken parts of the piston hitting the plug and closing the gap.[/b]
Thanks a lot for your help!
 

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You can't tell what the cause was just from the spark plug, so you'll have to take it apart to make a better diagnosis. If it was a lean burn down it could from plugged jets, water in the fuel forming ice in the carbs, an air leak from one of a couple of possible locations, or just the wrong jetting for the conditions. If the failure was from detonantion then you have to look at fuel quality and other possible failures could be from piston failure, broken skirt, and ring locator pin failure, and lose of lubrication and overheating, etc. Many possibilities to choose from and a great learning opportunity.
 

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any chance you can throw a picture up on the piston?? a hole in the top means your burning hot/leaning it out. I would agree with tuned,,, check over your carb boots. when these get old and brittle, they get air leaks in them and you take in more air causing a lean condition. good luck with it.
 
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