CONTINUOUSWAVE

Hello, and excuse me for referencing to my thread set up on an external site. I thought I'd reach out to this great community, since ContinuousWave has already helped me enormously through its archived repair discussion material, far exceeding the quality of guidance one would expect from an internet discussion board. I feel like I could maybe help someone by keeping a repair log and setting up a discussion here, though I'm still searching for some answers myself.

So, I would like to ask you to check out my thread at iBoats, where I have a report on my repairs and measurements, plus some video footage on the performance of the engine in question: http://forums.iboats.com/forum/engine-repair-and-maintenance/mercury-mariner-outboards/10418505-trigger-sticking-cause-of-low-rpm-at-wot-and-misfire-video

My question to this community is the same as in the end of the thread behind the link: how can I have such a low DVA voltage at the coils, but still get such a great performance from the engine? Should I start fixing that or not?

The change in the voltage you measure from the stator coils that occurs when you connect them to the switchbox is probably quite normal. With no load, the voltage output from the coil will be at its highest. With a load, the voltage output will decrease. I browsed your very long narrative of the problem and applied remedies. It sounds like replacement of the trigger box was the cure.

Variation in the readings you are getting from the "DVA" compared to the specified readings are likely due to variation in the DVA measurement. The factory book probably uses a standard commercial "DVA" meter. Unless you have that exact meter, the readings you will get might vary by probably 10-percent or more. The whole concept of "DVA" was some sort of a peak-reading AC voltmeter from the 1960's. In today's world, the specifications would just cite a peak AC voltage as measured by a modern digital voltmeter with a peak-hold function for AC Volts.

I must admit that I don't have any first-hand experience with these very old design electrical systems in the legacy Mercury engines. From reading about them, they apparently are notorious for problems with the stators, the switchboxes, and the triggers, and the durability and longevity of those components is not especially good. The CDI aftermarket parts seem to enjoy a better reputation. If you got the engine running well without having to replace all of the coils and modules, give yourself a pat on the back.

Thanks Jim for the input! I too have learned that the ignition components in Mercury outboards from that era aren't known as especially reliable. The CDI troubleshooting guide in this particular problem was actually more helpful to me than the Mercury factory manual: without the CDI guide I would have spent a lot more time finding the source of the problem (the trigger). Seems to me CDI really wanted to dig into this and start solving the problem, whereas the factory manual was printed in 1995, without the practical evidence on how individual components perform over decades of hard use.

Oh, and the DVA meter I used... I did the DVA adapter myself to fit my digital multimeter. This is the wiring diagram, super simple and the component costs were under $5. Note the polarity of components! I strongly recommend to find a small Tupperware box or similar to protect the electronics; playing around with the meter when the engine is on muffs and water sprays everywhere proved, that the small extra labor with the water resistant casing paid off.
https://www.circuitlab.com/circuit/25mk3x/screenshot/540x405/