A tip which might save your CDI
Sometimes it could be too late to notice if there is High Voltage discharge anywhere else except at spark plug. In some cases you have a visual clue such as arcing at connecting points of mechanical ignition switch , however in most cases it is not as visible or audible when engine running .
I suggest to try the following :
With the spark plug inside , and without fuel , turn on the ignition and rotate the flywheel by hand , keep your ear very close to the CDI unit , if the HV discharge is out of the spark plug ( either due to poor grounding or wiring issues - less resistance path beside the HV lead ) , inside the CDI you hear a faint click ( same sound as spark would make ), then you have a rouge HV inside the CDI. You might hear it both at the plug and inside CDI so ensure you pay close attention to catch it . If that happens ,it will fry up the capacitors and fails the unit .
Beside from checking the grounding , ensure the HV wire is isolated from touching any part of the engine except the spark plug. And ensure the lead tip fully touches the top of the plug the cap is plugged over.
Applying these preventative measures will ensure a longevity and consistent performance of the CDI unit on gasoline powered models 