Vintage Dirt Bike Q & A

I have a 78 cr250 and this spring when I got it out and went to get it running it had no spark. I changed the spark plug, tested the coil it was good, pulled off the cover and cleaned up the magnets (they were a little rusty) and it still had no spark.... then later that same day I went out to try it again and it had spark. And every time I started it that day, probably 5 times, it had spark. Then the next day I went to start it... no spark.... and eventually got spark later that day again same as before. Does anyone know of what would cause this? I have a different cdi box coming in the mail as I write this so hopefully that fixes it? I'm not sure if it will or not. Any help would be appreciated! THANKS

Probably the box or more likely the pickup coil down by the magnets. Gotta try something but the pickup coil can be ohm tested good/bad. Do this in the am when it is not giving spark.

Maybe a bad ground? Depending on humidity you may be getting continuity one day and not the next.

Take the whole electrical system apart. Inspect for cracked insulation etc. etc. Get all the parts tested against the specs in the factory manual. Don't have one? Email me. Rebuild. Use diazoelectric paste on all the electrical connections as it keeps moisture out and promotes a good electrical connection. Get it from PepBoys or similar. Use electrical tape to join all the connectors and then tape (not zip-tie) the connectors to the frame. Liberally spray inside the rotor housing with water-repellant. Maybe even silicone seal the cover and the junction where the wires come out. Buy a new high quality plug cap and silicone the connection to the coil. Grind the paint of the frame under the coil mounts where it is earthed. If the kill-switch looks less than 100% replace it or disconnect until you are sure it is not shorting out.

And while you are at it...check the letter on the rotor cover matches the letter on your CDI box.

Enjoy!

_________________
Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

got my new cdi box today and now i got spark!! woohoo!