I have a 1987 TRX 250X. I bought the bike from a friend who had just had the top end rebuilt with a new Wiseco high compression piston, Web cam (yeah I know not the best brand), new valves, springs, etc. After he got it back, it never ran right. He just thought it was a jetting problem. I messed with it forever, then took it to a local guy that builds racing bikes. He looked at it, and checked everything mechanical, including the carb, and found nothing wrong. It still won't run right. It will start on the first kick with no choke, but runs very rough, like it's bogging, but it's not. When held near WOT, it surges, and the RPM's go up and down, similar to a rev limiter. I was almost sure it was carb problems at the beginning, but now I think it may be something electrical. Has anyone else had a similar problem? Could it be a coil or cdi box? I'm totally mystified as to why it will not run correctly. Any help would be greatly appreciated.

 

Hey whats up. I have an 87 250X that i am building. If theres nothing wrong mechanicly than ur best be is somethin electrical. Id defiantly look at the coil and CDI box first. Since they control spark and how the engine fires. Over time a coil or cdi box weakens. So most likely either of them are wearing out. A factory coil isnt that much but a cdi box is gonna cost a lil bit. Or if u really wanted u could get a wiring harness from a 300ex. Ebay would be the best place to look for that. I bought a new coil but my cdi box is original still from 87. Hopefully ill get my motor finished by next weekend and bring it to life. Good luck and i hope this helps.

 

Well i talked to my brother about it and he said its something mechanical. He said its most likely something to do with the valves or the carb. So u really need to look it over again and see if its all to spec. hope u find ur problem.

 

Sounds like your cam timing is a tooth off or the chain is stretched in one spot.