How to test for a spark

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Here is a procedure from Reg from Bristol on how to test for a ignition spark, and CDI issues.

Standard CDI bikes have been known to suddenly stop with no warning and the rider finds there's fuel, but no spark on either side

The tests to pin down the fault take less time to do than writing this short procedure. (I'm sure I've written this before, but once more with feeling as they say)

First disconnect the kill switch wire and try again. (Just unplug the black/white wire from the CDI box. This bypasses the Kill Switch) Its been known for the weather to get in the contacts under the kill switch knob and this can short ignition power to ground. No joy? Under the seat are the stator and CDI connectors open the 2 way connector that carries the blue and white wires. Makes sure you have the wires from the stator, not the CDI box. A quick resistance test between the battery negative terminal ( GROUND) and each of these will indicate if the source coils on the stator are OK. Never mind the others for now. Quickest test is to measure between the the blue and ground and expect 500 ohms plus the slightly longer but more informative test is to check for 387-473 ohms on the white to ground and 77-95 ohms between white and blue. A more exhaustive test would be to measure AC voltage on the blue wire from the stator, and the white wire from the stator. The white (Low speed coil), should be about 90 volts, and the blue 100+. (Measure while the bike is being cranked.) Most people know this test by now, its the next bit that seem to go unheeded

If the stator tests out OK, then its probably producing power for the ignition system and you need to see if the CDI box is handling this power correctly. The tests in the manual require specific meters few if any will have and are a long winded PITA anyway which tells us very little we can do anything about.

There's a quick and dirty test you can do with a cheap common as muck digital meter to see if the CDI is healthy. I've done it many times to diagnose CDI failures quickly Basically you need to measure the 'open circuit' DC voltage on the LT wires to the coils 'open circuit' means the wires are disconnected from the coils. Unless its an auto ranging meter, you will need to set the voltage range to 0-250V DC DC OK? With the black probe clamped to battery neg and the red probe stuffed in an opened Coil wire bullet connector Crank the engine on the starter button for a few seconds noting the display then do the other side.

On a well running bike I'd see around 150V perhaps more On bikes with failed CDIs I've seen as low as 6v Often both sides, sometimes one when one side has failed

You will not get a steady reading ! The meter is trying to read pulses, most aren't designed for that so dont worry if it flickers about. Just test long enough to get a good indication/average of the ouput voltage.

If you dont get voltages well up in the 150VDC range, the CDI has likely failed and the options are:

Repair: if you're into electronics and have the patience to dig it out the potting compound

Replacement: But new ones are NLA and a 2nd hand one is a crap shoot

Upgrade: get an Ignitech

BTW I dont see why the DC output test couldnt be used to test a suspect Ignitech. Also, a kill switch leaking to ground will easily shut down an Ignitech as its just monitoring a voltage level on a pin Testing for a lost spark is, or should be, a matter of moments

And here is a post from Allan that may also help when you are stranded or out of ideas:

Reg, in the thread yesterday I suggested that the poster try disconnecting the 3 yellow wires, I know you wrote that the stator usually deteriorates over time and are not as apt to fail suddenly, but when I bought my first CX the guy I got it from said he was driving it and it was working fine when it quit all of a sudden, "just like you turned the key off", his exact words. It had no spark. I did the stator resistance tests and everything seemed OK.

Then after some more head scratching and reading on the www, I unplugged the 3 yellow wires and had a nice fat spark. There was a short in the charging circuit. I still do not understand why this causes the ignition to fail but it does.

There have been 4 or 5 cases since on the forums where the poster has said the bike quit just like you shut it off that have turned out to be the same problem. So I always suggest that people try this as a quick test, especially if they are broken down on the road and need to get the bike home. I know this was not the problem yesterday but it could have been, it only takes a second to unplug the wires and it might get ya home..

Once you have access to a meter you can do the voltage tests on the blue and white wires and resistance tests on the other wires including the 3 yellows. If you did not test the yellows and just assumed the problem was in the high and low source coils,,someone might buy an ignitech thinking that will solve the problem only to find out later the charging circuit is fubar.

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