Motorcycle Repair: 81 cb250n electrical problem, auto electrician, plug caps

Question
Hi Bill,

I have a 1981 cb250n that I am unable to get spark from. The problem developed about a month ago when the bike died suddenly while on the road. It was running well and had been serviced approximately 50km previously at the time. Initially I was able to get a weak spark but this has since also stopped. I have checked and cleaned all the connections/earths I can find using a wiring diagram, checked the fuses, dismantled and cleaned the kill switch, replaced the plugs, coil and finally cdi all to no avail. I am sure I have missed a faulty earth or connection somewhere but I would appreciate some help isolating the problem. I am certainly no auto electrician and my approach has probably been a bit too haphazard.

Any other suggestions you have would also be greatly appreciated.

Thanks

Answer
Dave, you mention replacing the CDI... just the control module or the whole system. Ignition is initiated by the pickup coil on the flywheel/stator unit. You need to see if that is functioning first.

Also check out the spark plug caps for open resistors inside. Should read out about 5k ohms and both be close to the same reading.

Note that the self-powered (doesn't need a battery) ignition switch puts a GROUND (earth) on the ignition to shut it off. When you turn the switch to ON, it actually opens the ground (earth) path. If you can disconnect the ignition switch and bump start the bike, it may fire up indicating a bad ignition switch. You can also disconnect the KILL switch for the same reason. Kill switch grounds out the ignition in the OFF position, rather than opening a hot circuit.

I don't have specifics on your machine, as they were not sold here, at least in that form.

Bill Silver