74 mx 250a spark issues

[fen880]

Hi got a mx 250 with spark issues ie sometimes it sparks sometimes it doesent  . I am starting to think the cdi unit is had it ,but in my experience cdi boxes either work or they dont ?  Anyone got any ideas on this

                         Cheers Ben

[TT5 Matt]

what temp is the motor when the spark dies

[fen880]

Usually when its cold

[HeavenVMX]

Bad earth? Have you recently painted the frame or engine and forgot to remove paint from engine mounts or coil/CDI mounts?

Run a separate wire from magneto backing plate to coil base and CDI box mount point to ensure a good earth

[fen880]

Buke hasnt been painted or anything just hasnt been run for at least 10 years i gave it all a cleanup but will give it another going over . Am i right in thinking that a cdi wont work intermittently it will either work or it wont ?
          Ben

[TT5 Matt]

electronics do funny things sometimes,if it was me id send the whole ignition system off to beta bikes or someone like that where they can test it on their test bences hot and cold,saves all the head fork

[OverTheHill]

at work we had an almost new one [same model], only weeks old & no spark. Being CDI & us still learning about this 'magic' spark in desperation i replaced all the connectors from the loom to the box & box to top coil etc--just used yamaha crimp on type that we had at work. Anyway, it worked & never looked back luckily for me. Sorry if that's no help 40+ years later lol but 'might' be relevant.

[micko]

I got a yza that is doing the same thing, pretty sure it is the igniter/pulse coil playing up.

[Rossvickicampbell]

check all the leads and connectors - had a wire break inside the outer sheath recently which gave me intermittent spark.

[Freakshow]

THrow it in the bin and buy a PVL for it.