402 running on 1 cylinder

[Texas_Dan]

My old Merc had been slow to fire the second cylinder but just after warm up the second cylinder would start working and work throughout the day.
It took longer and longer for it to get to this point, well this weekend it sputted a couple times all weekend but never fired up the second cylinder
Replaced plugs, verified wires, replaced coils new, no change.

Removed the CDI unit but replacement units are pricey, just needed to understand the trigger before I replace the CDI. Does the trigger send a different pulse for each cylinder? It seems not likely being there is only one lead from the stator area to the CDI unit but before I spend 250$ on CDI I want to be sure this is my root cause.

Mid 70's 402 Mercury, electric start, converted to long shaft. Compression test shows same on both cylinders. Swapping plugs between cylinders has no affect. Changed to B8HS from BUHX (NGK) still no change. Just no spark from lower cylinder. Have not tried to reverse coil leads, seems redundant with new coils.

[boats.net]

Need to test using a peak reading voltmeter and test stator output to switch box and trigger coil output to switch box. If good test switch output to ignition coils to make all test per specs in manual.

[Texas_Dan]

Thanks if I had the manual or access to the boat without traveling 2 hours I would do that. But that is not may situation, I have the CDI unit with me and could run test on it but the rest of the boat is 2 hours away.

I will look to see if anyone has volt meter tests that I can check out the CDI unit at my work bench.

What I was looking for was the actual purpose of the trigger, does it send a single signal each revolution of the 2 cycle engine or one message per cylinder.

Thanks for your response.

[boats.net]

The only bench test you could do is resistance test and that wont tell you if it is good or not.
Trigger coils signal when to fire each cylinder.