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87 cr125

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hello guys, i am new to this forum i dont have much experience with dirtbikes. i recently picked up a 87 cr125 from craigslist as a starter bike. the previous owner had it sitting in his garage for 7-8 years. he did a top end rebuild before i bought it. after riding it for like 10 mins i noticed it seemed to loose bit of power. kind of bog down when you give it throttle. next day when i went to start it it wont fire up, i narrowed it down to low compression i pulled the jug off to find the piston ring seized to the piston. the piston looks almost brand new possibly less than 2-3hours, wiseco 54.50mm piston, the jug looks like it had a fresh bore job and honed real good. i had the jug looked at by a local bike shop they said the jugs good.

i been looking at a new piston kit, all the wiseco says "power valve need to be modified for oversized pistons" is there somthing that i need to do or the previous guy that did it possibly didnt do? as far as i could see the power valve does not protrude into the cylinder. is there somthing i am missing guys, any inputs?

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Take a magic marker and color the face of the powervalve and cycle the piston up and down slowly with the kickstarter a good number of times to rule out if its hitting the powervalve or not

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Is 54.5 standard or over sized? If it is standard, then the powervalve wouldn't protrude.

54.00mm is the stock piston, what i pulled out of it was a 54.50

Take a magic marker and color the face of the powervalve and cycle the piston up and down slowly with the kickstarter a good number of times to rule out if its hitting the powervalve or not

hmmm i will give that a try tomarrow, thanks guys for the replys

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Stock cylinder was also hard plated that year (first year for the 125) so I wonder if it was bored out correctly and the cylinder was replated. Unless it was resleeved with a steel liner is something I would check into. It's not common but sometimes owners get cheap and just bore it out the next size over and hone the cylinder up thinking it's all good and it's not.

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