Q: Do you know anyone who can check or test CDI units? And what are the obvious symptoms if a CDI unit is faulty?
A: The usual symptom for a faulty CDI unit is no sparks at all, as opposed to occasional sparks or sparks at the wrong time. Other components in the system include the pulser source and ignition coils, as well as electrical connectors and wires, and one of these is probably more likely to be the culprit. I suggest that you get hold of a copy of either the genuine Yamaha or Haynes workshop manuals as there is a test sequence to follow to determine where the ignition fault lies, and the correct electrical resistance readings you should have.