2010 Ec 300 scuffed piston and lost compression

[Bark3rd]

recently acquired a very low hour 2010 300 from a good friend that has been stored for several years I estimated had about 25 hours on it. refreshed everything rebuilt carb changed all fluids it ran very well except for a Rich break up from the middle to the top of the power band. it ran very well off the bottom and no other signs of things that could affect corporation other than the jetting. based on conversations with JD jetting and some research here I went from the 180 Main to a 178 to 175 then to 172. The 172 finally got the bike too accelerate mostly normally from mid to top also using a JD red needle clip and third position. at the end of the first day of riding with the 172 about two hours in after a few long straightaways bike bogged then installed then would only idle momentarily then shut off. pulled pipe and Reed cage identified cylinder plating looked undamaged but scuffs on exhaust side of piston. altitude is 700 to 1300 feet hot humid Texas. JD Tech said there may be something going on with the power valve to cause it to act rich can someone direct me to some information on what that means so I can address it during the rebuild. any input on anything I'm not thinking of greatly appreciated thank you.

 

[Hellcat]

Sounds strange . I would say when you take cylinder off look and see if the power valve was sticking . Be sure to disassemble it completely and clean all burnt oil off and lubricate it good . Most guys run 50:1 but I always ran 32:1 . Little messy on silencer but I can deal with it and my bikes run good with it . Also measure cylinder bore and check piston size . Gasgas used 3 different size pistons for some years . Cylinder will have a - A,B, or C on the lower flange area . I just rebuilt a 2010 and found B pistons but the bike had a A cylinder . I ended up using another b cylinder I had . The difference in size is just a couple thousands but if piston is to tight this could cause piston damage when it got hot

 

[Hellcat]

Also the 2010 I just picked up sat for long time and kid bought it before I made deal. Well kid ran it with old air filter that was falling apart from old age and sucked it all in and then leaned the bike out and over heated it and killed bottom end . Wonder if your bike had a old air filter and it was cranked and ran and sucked in old pieces before a new filter was installed to sell it