[jimbo1073]

will this mark on this piston affect anything??? its like brand new. rebuilt motor and can not get it to run right. misses in mid range and no top end. changed the whole electrical system rejetted many times. up to a 178 now. before rebuild and bore i was running 168 main jet. new reeds also. ive rebuilt this motor several times and never had this problem. should i rebuild the carb? what can possibly cause it to run this way. its runnin lean but when i move the clip to the leanest position(top groove) it runs better.still not good at all. ? 87 trx250r fmf pipe, 80over wiseco piston,cool head (21 dome), no airbox lid, Vforce reeds

 

[StrokedTater]

i would noit run that. that deep gouge is on the weak spot, the skirt. thats where they are likely to break and urs has some damage there now. a lean condition can be cause by an often overlooked airleak. base gasket, intake gasket, carb seal, intake boots, crankshaft seals, head gaskets, cases. i would be certain that is all selaed up well and in good shape then go from there.

 

[John Tice]

Do a close proper measurement of the Skirt Clearance. Maybe too tight or maybe too loose. Check the piston manufacturers fit recommendations, use a Dial bore gauge.
JT