Nissan 9.9 not starting-not always having spark

Hello all, I have a Nissan 9.9 2 stroke motor that doesn't always start because of no spark. On some days it will start right up, runs fine, no missing or issues, but then the next time I try to start there is no spark what so ever, very frustrating. It has the electric start also. My question to anyone out there is, where do I look for what's causing this condition. I believe that it might be the CDI unit, but I remember from my dirt bike motorcycling days that the CDI units either worked or they didn't. Anyone out there have any ideas ? Thanks, Alan in Pa.

Start with a service manual, available at any Tohatsu/Nissan dealer. Then diagnose the ignition. The CD box is only 1 part of that system. Intermittent electrical failures can be maddening to troubleshoot, as they seldom will fail while you are testing -- and if it ain't broke, you can't fix it. One tip: Verify all ground connections.