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Discussion Starter · #1 ·
Well, last monday I went for a nice long trail ride. Day started as usual. My 97 ZR 440 fouled out her usualy two plugs right after getting warmed up. Has happend as long as we've owned the sled. But after riding for a while it started to foul a plug, then it cleaned itself out. All day it would do this and sometimes it would outright foul the plug to where you had to change the plug. I ended up fouling 5 plugs that day. I questioned water in the gas. not sure though. After riding all day, I made it almost home when riding at about half throttle the motor seized and quit. Completely seized, would not rotate, then after allowing it to cool for 15 mins or so it came loose and rotated again. We trucked it back to the garage and ran a compression test on it that revealed that I had only about 60psi in my right cylinder. I ended up burning up the exhaust port side of the piston, and severely scratching the sides of the piston. Not sure why though. I'm questioning whether or not it ran lean. I have it jetted for 93 octane fuel according to the jet chart that came with the sled. Basically what I'm asking is if anyone out there might have a reason for something like this to happen. I'm baffled as to what caused this. I have the sled rebuilt already, started it up today and it would run, but only if you held the throttle slightly open. Would not idle on its own. So currently I have the carbs off and torn down. I recently cleaned them, but am going to reclean them, and then possibly jet it a size or two bigger. Any help here would be greatly appreciated. Thanks
-Chris
 

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Discussion Starter · #3 ·
ok, the plug on the left(side that didn't burn up was medium brown. theone on the right is a shade of gray. The difference in color is what caused us to think it ran lean. But could it have run lean on oil, or gas? The burnin on the top of the piston would mean gas wouldn't it? But why would it score the sides of the piston so severly. I'd attach a pic of the piston, but the files too large to post on here.
 

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It mixes the gas and oil before it hits the cylinder. I'd go up one size on the main jet and possible move the clip on the slide needle down one slot.
 

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the gray on your plug is your piston from when it melted. exaust side is a line burn skoring of the piston skirt depends. if its on the intake side your injesting snow. if it is on the exaust side when your piston started to melt it would have started to skor the piston
 

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yamahamm700 said:
the gray on your plug is your piston from when it melted. exaust side is a line burn skoring of the piston skirt depends. if its on the intake side your injesting snow. if it is on the exaust side when your piston started to melt it would have started to skor the piston
He said he had it rebuilt already. It should be Ok now, just jetted too lean on that side.
 

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Discussion Starter · #7 ·
yeah, the sleds all rebuilt and ready to go motor wise. I just recleaned my carbs and rejetted them putting new mains in (bigger) and i also put new pilot jets in just in case those were dirty. since they're so small its almost impossible to effectively clean them. so, now i just have to get the time to put them back on. don't have enough free time when i need it for something like this unfortunately.
 

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I would have done something with it when I bought it so it didn't foul plugs all the time
 

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Discussion Starter · #9 ·
we've messed around with this sled so much since we got it. we finally figured our part of the prob was we ran 87 octane in it, we rejetted it for premium and it made a hell of a difference. either it was dirty gas, watery gas, or just not enough octane, we really don't know. it fouling a couple plugs right while warming it up isn't that big of a deal. you can buy a plug cleaner and clean them back out when you get the time.
 
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