YZ125 lost power then no spark, any ideas?

[J. Lewis]

I've been trying to get this '89(approx.) YZ125 to start and have tried everything I can think of without throwing parts at it. I even tried another coil that I had but that didn't help.

Basically the bike had started to lose power and run bad and then one day wouldn't start at all after sitting for a while. All grounds have been checked and there is still no spark at all. The magneto wheel was pulled off and everything has been cleaned of rust and corrosion.

I've checked a few things and when kicking the motor over repeatedly the coil is building up voltage but it apparently never triggers to make the spark(i.e. the voltage should build and then drop at each spark event correct?) The fact that it builds voltage makes me believe the magneto is not bad and that the box is the problem, any ideas? I suppose the magneto could be creating voltage but that the triggering part of the magneto is bad? Talking out of my ass here, sorry, don't have much experience with magneto ignition.

TIA,
John L.

[odaen]

sounds like it could be the CDI. there are wires that you can measure the resistance of to make sure a coil (like the stator and such) aren't opened or shorted. i'd go to the manual section here and download one if it's available. they'll spell it out, including what color the wire is.