I need some help. I've got a '93 RM 125. The motor will misfire whenever you pass 1/2 throttle, and the further you go the worse it misses. It will run fine throughout the RPM rangeas long asyou're easy on the throttle. This problem has slowly started and gotten worse. I've pulled the carb, cleaned it, put a new correct plug in it, put a new top-end in, cleaned and adjusted the exhaust valve, now I'm kinda stuck. Like I said, it ran great and slowly developed this problem. Anyone have any ideas?

 

If you are sure that you cleaned ALL the small passages in the carb(especially the main jet passage) i would take a close look at the coil & associated ignition components. As ignition components begin to fail, they lose the abilty to build a chargeat higher RPM's.
Good Luck,
Harry

 

Ok, I got a carb rebuild kit and re-built the carb with new gaskets & bolts, and cleaned the whole thing so it was spotless-took out the jets, cleanedALL the small ports, and so on. Same problem, if fact it runs worse.

What would you suggest as to test the ignition?

Besides the ignition failing, the only other thing I can think of is exhaust not clearing the spent gasses out (maybe the packing in the muffler is soaked with carbon), therefore choking the motor-any thoughts? I need to get this thing running! Thanks for the help