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Piston slap

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My engine was built by ken Oconner racing. I have noticed that off the pipe but about mid throttle that I have piston slap. I'm running 93 non eth fuel. 32:1. Zuk needle with a 168 main and a 42 pilot. I was wondering if it could be timing issue. I have no experience with timing a 2 stroke.

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Piston slap is a rattle that is most prominent at idle speed.  You must have something else going on.

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'off the pipe' and 'mid-throttle' doesn't quite sound right,

on a YZ250, I'd think by 1/4 throttle you'd be into the powerband.

 

If you meant re-accelerating while in a gear high (lugging) then I'd suspect detonation rather than piston slap noises.

 

Since you're already using 93 octane gasoline, sounds like you might have to correct the squish band height.

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Yes sorry. Only while lugging. 3rd gear or higher. I have access to 100ll fuel. I thought about mixing a couple gals in to see if it helped.

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Increasing the octane is just a band-aid,

either stop lugging or, if it hasn't been done yet correct the squish height. (known issue with the YZ250)

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