I have been chasing this problem, or possibly a few different problems all causing the no spark condition, since last August.
I checked cranking speed with an optical tachometer and found it to be cranking too slow. I disassembled the starter motor and found that the bushings were worn and the armature was rubbing slightly on one of the magnets. It now has a new starter and starter relay.
I found voltage drop through the battery to starter cables to be too high, so I replaced the cables with new, high quality marine rated cables.
After this, I verified that the motor is cranking at just over 300 rpm.
I replaced the optical sensor after the motor died while running once and would not restart. I identified the optical sensor as the culprit using the CDI no spark troubleshooting guide. The motor ran after replacing the optical sensor.
I have probed the black and yellow wire when the motor is exhibiting the no spark condition, but have not found any paths to ground when the key is on and the safety lanyard is engaged.
I have verified stator output using a peak voltage adapter.
I have tried disconnecting the voltage regulator and cranking. Still no spark.
I verified over 150 v on the black and yellow wire at power pack while cranking with the peak voltage adapter.
I had less than 11 v at the yellow and red wire, measured at the starter relay lug, when cranking with the key. I then hooked up a remote start switch that jumps power from the main starter cable to the relay terminal, and verified that voltage is over 12 v at the yellow and red wire when cranking using the remote start switch. Still no spark.
I have now ordered a new CDI power pack.
The troubleshooting tests I've been using are in the installation instructions PDF document located at this link:
https://www.cdielectronics.com/product/113-4985/