TOPIC: This one took me back to school!!

I had a good one come through this week & wanted to share it with everyone.
1984 850 4 cyl with cdi. (solid state distributor)
I 'thought' I had it figured it out initially from the owner's explanation that,...'It ran fine until I go full throttle - then it would quit."
Initially I suspected fuel delivery, found a faulty fuel pump one-way valve - replaced it and the diaphragm and thought I had won the battle.
NOT!!!
The beast would start and idle fine, shift without stalling, accelerate perfectly, and run along fine at above half throttle. But,...If I went to wide open throttle (WOT),...I would get anywhere from 15 seconds to 40 seconds (+ or -) of flawless performance,...And then Kah-Pow!!! Instant shut-down. No faulter, no sputtering or warning - just instantly dead,...Coast to a stop,...Move the throttle & shift back to Neutral,...And without re-priming the prime bulb,...Instant re-start with flawless idle, shift & acceleration.
To safe time on guessing the cause,...
I confirmed that I had 12vdc on the 'key-on' white continuous through the shut-down.
I confirmed I had 12vdc throughout the shut-down on the red 'constant 12vdc.
I confirmed I had 100 volts +/- on the green coil lead from the switchbox, when the appropriate scale would be 75ish-120ish volts.
Obviously,...The culprit has been narrowed down to a couple of components,...Providing I did my testing properly.
What are your thoughts & reasonings as to what the cause of failure is???
This is not to critise responses,...This is to learn a valuable lesson for your future trouble-shooting of these way too cool old Mercs.
I will respond with the cause after a few post suggestions - or which way you would go to attempt a resolve.
I 'did' win this battle with the Merc, and will explain in a day or so.
My solution was actually a point of study and research by Mercury Marine back-in-the-day, that involved women. (hint-hint) No joke.
Doc Frankenmerc

Not a clue here but I'll be anxious to hear the cause. Nearest thing I had to this was an OMC stringer V6 outdrive that would quit at just about planing rpms. Turned out to be a faulty "shift interrupter switch" that OMC utilized, that was supposed to cause the engine to miss momentarily and drop the rpms when shifting from neutral to forward for a smooth shift. Instead, it was activating at about 1/2 throttle and shutting down the ignition.

Bad seal on female fuel line connector sucking air at higher RPM's?

back in the 70's i found that new merc had the pin on the fuel connector to short from the factory tha drone me nuts.mercury call me for the problem.

Woman reach up to hold hair when going fast and pull out kill switch?

cut out mercury switch......hi spd stater coil.......ummmmm?

I know, but I'm not tellin!!!!!

My money is riding on Daveswaves.

No right answer yet.
All good answers though.
Ponyboy, no high side on the stator on the solid state distributor style ignition. That stator just charges the battery.
Tomorrow I'll post what it was, but would still like to hear others' thoughts on this one.
Doc

how bout a hint

Well with issues like that you have to determine if it is ignition or not, and if it is ignition it will quit suddenly with no warning. Usually fuel problems will cause the engine to nose over first and not just stop suddenly. One way is to have a helper drive the boat while you sit back next to the engine with a timing light attached to the plug wires, and see if the light quits at the same time as the engine does, and take it from there. I used to see a lot of trigger wires break inside the insulation where they flexed, especially if they were not fastened correctly, and when the throttle was opened out the wire insulation would stretch pulling the wires apart inside. Instant shutdown. Pull the throttle back, the wires touch and she starts right up again, till you open the throttle once more. Always wiggle and pull on the wired during testing to see if the engine reacts, especially wires that normally move in operation. For fuel issues, try looking down the carb throats during running with a good light to see if the fuel discharge changes when the engine quits, or hit the choke for a moment during the nose over to see if it picks up for a second. Suspect fuel delivery if it does, and check that the portable tank is not sitting on the hose!!

George,
I was betting on you or the Professor, and you nailed it.
Although I tugged on the wires coming out of the trigger - thinking the same as you are, and not seeing failure, the timing light attached at WOT confirmed it was ignition, and process of elimination confirmed it was the darn trigger.
I wasn't able to confirm whether it was the wires being stretched at WOT or something internal, but the trigger was the culprit.
I was pretty sure it wasn't fuel related when I could instantly restart the beast without squeezing the prime bulb or using the choke, but the results pointing at the trigger really threw me for a loop.
Thanks everybody, for chiming in.
Thom
Doc Frankenmerc Keeping 'em alive since 1965

I thought a 1984 motor would have been an ADI motor, was that a typo?

Probably, as there was no dizzy equipped engine in 1984, unless it was, (ahem) a Frankenmerc! Merc wires left something to be desired back then, and you should always check the condition of them in any one from that era when looking for trouble, very common to find that is usually the problem!

You guys got me!
I meant to identify the beast as aa 1974 - not 1984.
RATS,...Now I need to go sit in the corner.

Doc F

Thanks to all that helped on this problem. I have been helping a person with there 72 800 and he has been having just about the same problem with his motor. After looking at his wiring I told him he would need to fix all of them and then it would be easyer to figure out the main problem. Once again many thanks to all, Skip.