Electrical problem w 98 RM125 no fire?????

There are basically 6 parts to the ignition on a dirtbike. The flywheel rotor, the generator and pulse coils, which are on the stator plate under the flywheel, the CDI ignition box, the coil and the chassis wiring.

The flywheel spins, which produces electrical energy in the generator and pulse coils, that is then passed to the CDI, and then onto the coil and through the plug wire to the plug. There are specific resistance values for many of these components that you can find in a service manual, but simply put if you have output from the stator, but nothing coming out of the CDI to the coil, or from the CDI to the coil, but not to the plug, you can isolate it to that component.

The service manual would help, but check to see if you have output from the stator. If no, pull the flywheel and find out why, if yes, check to see if you have output from the CDI. If that checks out, you may have a bad coil, or a bad plug wire. It could be as simple as a loose plug cap. A bad kill switch or wiring can even cause a no spark condition, as it grounds the spark continuously.

Dirtbike ignition systems are fairly simple, and relatively easy to troubleshoot, but the parts are expensive, so a little time with a multimeter and the service manaul specs can go a long way to solving the problem, and saving the cost of replacing expensive electrical parts