88 35 HP Mercury Outboard Not Firing Correctly

So on the last step of rehabbing my Grandpa's 1988 Starcraft with a 35 HP Mercury Outboard (Serial# 0B327135). After the rebuild of the actual boat we got the motor running no problem, just needed to clean out the carb and she ran on the ears for a good 10-15 minutes with no trouble. Fast forward to taking it out on the water. My cousin backs it off the trailer and parks at the dock while I park the truck, the whole time it is idling perfectly. I start to walk to up and it dies and won't stay running after that. After it sits for a bit it will start and run for maybe 30 seconds while it is idled up and then it will slowly start sputtering and dying. Figured it was fuel related and kept messing with the primer bulb, and eventually it breaks(stops holding fuel from going back in the tank). Take it out of the water and replace the bulb, still have the same issues. Pull the spark plugs and they're coated in fuel. Start testing the ignition system as a result. Pulled kill wire and checked resistance on the coils and trigger as well checked all wiring. After reading about all the switch box failures I go ahead and order a new one. Once it gets here I start pulling things off to replace it and while I have the coils off I pull the little protective rubber booty's off and see the magnets are cracked, so I go ahead and order two new ones since they are much cheaper than the box($25 a piece vs $150). After replacement it is till not running right. Finally get a hand with the GF turning it over while I watch the spark checker. The spark is still very intermittent on both cylinders. Sometimes it is a very strong spark, and then other times it stops firing altogether. Then I stumble upon this post:

http://www.marineengine.com/boat-forum/showthread.php?425077-how-to-diiagnosis-intermittent-spark

Which has not only resistance figures for the trigger but also checking both sides to ground. One side is definitely testing to ground while the other is open, which I find weird since I can test resistance between the two but only one side is testing to ground. I assume this means it's bad but I'm not sure as the graph doesn't state what it means if the trigger doesn't fall into the spec.

So a few questions:

1. Does one side of the trigger testing to ground mean it is bad?

2. Can these be repaired? I assume these function just like a crankshaft position sensor but it seems it is a sealed unit. It seems no one makes an aftermarket version of these and all the one's I can find are listed much higher than their MSRP and while can find some used ones, the cost savings are not significant enough that I would just rather get a new one.

3. Does this sound like it is most likely the trigger or the more common switch box?

Any help would be greatly appreciated as I am trying to get on the water before the end of summer.

The trigger on this model, being a two cylinder, only has "one coil". The coil produces AC power when the magnets located on the flywheel pass the trigger coil (magnets on the outer part of the flywheel power the stator, and on the center hub to power the trigger). As the flywheel turns the magnet passes the trigger coil and it produces the positive portion of an AC (sinewave), when the next magnet passes it completes the (cycle) and produces the negative portion of the wave. The two magnets are 180 degrees apart so the (timing) is symmetrical.

That voltage is fed down to the switchbox (actually one of two switches, but they are "in the guts of the switchbox") to "trigger" the release of power (from a capacitor, likewise integral to the switchbox) to the sparkplug coils - the positive portion of the wave triggers #1 cylinder and the negative #2.

Because it's a single magnet and a single coil, "that portion" of the trigger either works or doesn't work - so spark to both or no spark/weak spark at both (which is what it sounds like you are seeing). If one spark is good and the other crappy, it's not the trigger.

So the trigger could be your culprit - but so could the stator (also the coils and switchbox, but you have replaced both and "hope" that they were serviceable when you installed then).

With the funky reading you got on the trigger, before I went and replaced it, I would inspect both of its leads. Look for cracked/worn/rubbed/broken casing on the lead wires which may be allowing it to go to ground. Best check before replacing an otherwise good trigger.

But do also test continuity (at least) on the stator. You don't want to replace a trigger and find that the stator was bad. You can simply test for continuity between the two leads from the stator - you are looking for no more than 180 ohms of resistance. If you have "more resistance" then it should be DVA tested for correct voltages (can be done "at home" with a DVA adapter/multi-meter or by a DVA meter - most small engine shops even if they aren't "marine" can test the voltage).

Graham:

You've outdone yourself in clarifying the situation!

Jeff