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Work from the spark plug out checking components, and yeah, check that the kill switch doesn't have continuity across it with out being pressed.  

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If you have a multi meter that can read AC volts and continuity you can do some basic trouble shooting. 

First inspect the kill switch and wire all the back to the CDI or coil. If its pinched or grounded anywhere that has to be fixed. If thats good move on the coil wire and spark plug boot. Many a no spark has been caused by a problem in the coil wire or plug boot. There could easily be crack or corrosion in the wire. 

Now you will need the multi meter. I recommend starting with the stator. It would help if you have specs from the service manual, but even without them you can do some diagnosis. The stator has two different different coils in a CDI system, both send AC voltage to the CDI box, and both will have a specific amount of resistance that the meter can read. The one under the flywheel is the charging coil, it charges the CDI. The one outside the flywheel is the trigger coil, it gives the fire signal to the CDI box.  Identity which wires coming out of the left side cover belong to which coil, if you have and older CR with only 4 or 5 wires its pretty easy, you might need a manual with the newer ones, they have a lot going on. Check both coils for continuity. They both have a specific amount of resistance that they should have, but even without knowing that you can do meaningful tests. If a coil tests as open or infinite resistance, it's bad, a wire is broken somewhere. If the resistance reading is in single or low double digit ohms it likely has an internal short in the windings. If a coil has continuity to ground (the engine case), its probably bad. Trigger coils never have continuity to ground, and generally the charging coils don't either. 

If you don't find any obvious problems with the resistance and short to ground tests you can check the AC voltage output from the coils. I don't know the output specs for the CR, but the trigger coil is usually in double digits AC voltage and the charging coil is high double digits or 100 volts range. If the charging coil output is lower than the trigger output thats a problem.

The coil is pretty easy to test. The primary windings (small wires from the CDI) should not be open, shorted to ground or the secondary windings. The secondary should have a pretty high resistance reading, continuity to ground, and No continuity to the primary windings.

this is a generic AC CDI diagram:maxresdefault.jpg

 

You can test the output from the CDI to the coil by reading the AC voltage on the two wires going to the coil. If you have good inputs to the CDI and no AC voltage to the coil there is a CDI failure

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