Motorcycle Repair: 83 honda cm250c no spark, coil windings, plug caps

Question
I have a 1983 HOnda cm 250c with no spark. Coil and pulse generator checks out. All wiring and connectors on the ignition system check out. The ignition and kill switch circuits are ok. I can't find new cdi units for this bike but have purchased two used ones. Still no spark. The Stator checks out ok with tests from Clymer manual. I am getting 22 volts from generator to cdi unit. Is that enough? Are there any tests for the CDI unit. Help!

Answer
Greg, it would have been helpful for me to know the values of the coil and pulse generator.

http://www.cmsnl.com/honda-cm250c-custom-1983-us_model7282/partslist/E++09.html  you should be measuring the small 2 pin connector that goes to the pulse generator coil. Ohms readings should be in the .5 to 3 ohm range, with voltage outputs around 2-5 volts AC. The pulse generator coil is a timing circuit for the CDI module that is getting power from the charge coil windings on the stator. If you don't get a small voltage signal from the pulse generator, the system won't operate. Pulse generator failures are not unheard of.


Check primary windings of the ignition coil, which are probably down around the .5 to 1.5 ohm range. I don't have a shop manual for a CM250 for specific resistance values.

Check spark plug caps to read out about 5k ohms. ALWAYS check spark with both leads grounded to the engine. A double-ended coil has reversed spark polarities on one spark plug, due to the design of the coil secondary windings.

Bill Silver