engine rebuild problem

[genericmic]

just had engine rebuilt(new piston rings etc and bottom end) now have problem of running really rough at low revs then hitting a power band and running great at mid revs and then not pulling as revs increase further. jetting etc is same as before rebuild and have checked carby and seems clear and new fuel used. any advice would be appreciated. steve

 

[hasBen]

What year and model is your bike? It kind of sounds like an exhaust valve problem.

 

[genericmic]

its a '97 200. nothing else has changed since before engine rebuild. local mechanic(not the one who did rebuild) suggested riding at high speed/revs to try to "clear" out the system before doing anything but i dont think that is going to help! dont want to do any damage before i find out what is wrong.

 

[jaguar]

sounds like it was jetted for the poor mechanical condition and now that you have good compression you need to rejet it.

 

[hasBen]

Hi Steve,
jaguar brings up a good point.. sometime in the bikes past it may have been jetted to compensate for its worn topend condition. With a fresh topend it may well need rejetting. I had this happen when I rebuilt a Can Am 175. However before altering the jetting just check a few things.. make sure the air filter is cleaned and well oiled. Had your mechanic checked the exhaust port and pipe to see if it was carboned up? Check for air leaks. I mentioned once before in this forum about how the exhaust valves were installed incorrectly in our '86 KDX200 by the shop who rebuilt it before we bought it. It ran similar to the way you described yours. I finally set the valves up with common sense (still not sure which is in error, manual or valve markings) and the bike ran much better. It ran better still with a little change in jetting. I am sorry I can not be more helpful. Perhaps someone else has some hints to lead you in the right direction. Good luck with it. Ben