Detonation - RM125

any idea how this happened? i checked the plug the other day and it was running rich. blew up today, checked the plug and it was white. this is what the piston looks like. its the side opposite of the exhaustphoto_zps993d9a49.jpg

Pump gas

Octane changes every tank

ive used pump gas ever since ive got the bike. I started using 91 ethanol free since winter though. I got lazy and got 91 with ethanol from a gas station. That could be it? I get the better stuff from an oil company that doesnt share a pump with different octanes.

Not the ethanol 91 is 91, no matter what the fuel makeup is.

 

 

Fresh fuel and a issue like you have is a possible bad left seal, massive air leak or improperly mixed fuel.

 

 

Hint:P When I buy fuel at a station with one hose for all grades, I put a gallon in my truck tank (to flush out the hose) then I fill my can.

left seal as in the flywheel side?

left seal as in the flywheel side?

Yes. Allowing air to be sucked in and run lean. A failing crank main bearing can also cause this.

the seals are good. i did the top end without fixing the detonation damage and it does not idle. could it be from the damage? the head is pretty bad, but the cylinder isnt too bad. should i pull it all apart and send both the cylinder and the head off or just the head?

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