CDI Problem, I think

[Brad70]

While riding my 1998 RM125 suddenly started running very poorly, a lot of top end noise, no power, stalled whenever I let off the throttle. I tried a new spark plug - no differnence. I only have had the bike a few weeks, so not knowing the condition of the top end I tore it down, everything looked OK, the ring gap was a little wide but not bad. I inspected the exhaust valves, reed valves both were OK. I inspected the carborator, the float was low, but everything else looke OK. I convinced myself the problem was ignition. I pulled the flywheel and the key was OK. I have a decent everyday multi-meter (ohm meter) and checked the coil, the secondary coil was lower than the range in the service manual, but I doubted that it was enough to casued this condition. I checked the CDI unit, atleast 25 of the 40 some resistance tests were bad. Obviosly I think that is the problem, but wanted to run this by someone with a little more motorcycle experience to see if this sounds logical.

thanks,
Brad

 

[uts]

I have been told that the only way to check a cdi unit is to install another one and see if it fixes the problem. Do you get a strong spark at the plug when you kick it over. Have you put the bike back together again. You may have lost compression due to a blown head gasket.