Whats Wrong Please Help!!!

[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

[C-LEIGH RACING]

What does the cylinder bore look like & how much compression does it have.

That piston looks ok on that side, just a little smoothing out like if that scratch has an edge & use it again.

Do you have the spark plug gap set at 0.18 ~0.20 for the stock ignition system ?.

Dont let the ignition system fool you, to thinking its jetting, even though it is a new ignition system it can still cause an upper rpm skip. Rule that out first & then go to the jetting.
Check the silencer as well, make sure the cores not broken loose & blocking the exhaust.

A test if you think the carb could be flooding or jetted to rich.
Start the engine, run a few seconds if it is COLD, then turn the petcock off & as the carb bowl fuel level gets lower in the bowl, the engine will start running better or start reving high, when as before it was getting to much fuel & couldnt run right.
Shut the engine down quick if it does that & then pull the carb & go through it, clean & check everything.
If gas has ever ran out the over flow tubes, that is a sure sign the carb needs attention & could very well be flooding the engine making it run like crap, but check that ignition first.
Neil