YZ250 piston questions

treybird189
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treybird189
Edited Date/Time 8/27/2020 9:11am
I picked up an 07 250 that was “rebuilt” recently. I decided to tear it down anyway to see what was going on with the bike, make sure everything is right and so on. The burns and deposits on this piston are weird to me. Does anyone know what would cause this?


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Paw Paw
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Paw Paw 8/24/2020 3:10pm
8/24/2020 3:10pm
What does the underside of the piston look like?

Paw Paw
treybird189
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treybird189 8/24/2020 3:25pm
8/24/2020 3:25pm
Paw Paw wrote:
What does the underside of the piston look like?

Paw Paw
Completely normal. No odd wear spots or cracking or staining.
FGR01
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Fantasy
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FGR01 8/24/2020 5:36pm
8/24/2020 5:36pm
Post a picture of the very inside of the piston, the bottom side of the dome. Try to make it a clear as possible.

Can we get a picture of the plug and inside of the head also?

Is that an Acorn nut on the cylinder base stud?
DB505
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DB505 8/25/2020 1:14pm
8/25/2020 1:14pm
Normal!

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15tc150
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15tc150 8/25/2020 8:33pm
8/25/2020 8:33pm
Uhhhhhh..... normal to have a burn patch like that?!? Lordy, i has neva seen a piston come out like that, completely clean in some spots, and polished looking carbon build up like I’ve never seen, guy must have tried to remove the carbon ontop of the piston during a re-ring, but didn’t do a very good job, that’s one severely odd burn, and as stated before, what’s the head look like, is it damaged at all?
TheTwostrokeTaliban 8/27/2020 9:11am
8/27/2020 9:11am
Looks like a mixture of an oxygenated race fuel and a shitty pump gas, and it cant figure out if it wants to clean the piston, or leave it full of deposits. combined with something like a blended oil like 927, so it cant decide if it wants to flash or varnish. haha. About all you can tell without seeing the combustion chamber, bottom of the piston, and a plug chop.

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