40TLRB CDI unit

[DougBradlow]

How do you know if your CDI unit is failing? Is their any way to test it to see of it is working properly? I get an intermittent sputter under a load not quit on plane but if I hold the throttle open enough just to keep the bow of the boat up but not on plane my engine has a sputter/miss. I changed the plugs and gaped them at .40,cleaned and rebuilt the carbs. Those CDI units are like 500 bucks,I hope its not going bad. Other than that it has plenty of power and idles perfectly. I just did a complete 100% rebuild on this engine and it has even compression on all cylinders.What could be causing my miss or sputter?

[boscoe99]

Bad news is that there is no definitive test for the CDI. Good news is that the CDI would be the least likely to cause your problem.

My bet would be fuel system related. Try misting a bit of gasoline into the air intake system when the problem occurs and see what happens.

I owned two Mercury two strokes. Both felt like they were running like crap at about 1500 RPM under a load. It was the nature of those beasts.

[99yam40]

You can test voltages into and out of the CDI before and while the problem is there to see what is in spec and what is not.
Service manual and a DVA adapter and regular meter or proper peak reading meter for reading these ignition systems is used
and the manual list minimum peak voltages so the can be higher with no problem.

Also check to see CDI is advancing timing properly and link and sync is done properly every time carbs are put back on