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25 hp Mariner runs briefly then no spark

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bastormer

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Have a 1991 25 hp Mariner. Ran begining of season. After half hour trip stalled would not start. Now starts runs briefly (5 mins), smokey, stalls then no spark and will not start again. Maybe days later start run brief then nothing. Had the coils checked at autostore said ok. Its always missed some never run real smooth. Always means this year and last. Before that sat for 12 years. Rebuilt carb last year. Switchbox? I actually was surprised when I had no spark would have sworn it was a fuel system problem. Turning it over is throwing gas/oil thru the motor out the exhaust can see in the water.
Everyday I look out, there it is at the dock mocking me! I hear these are pretty good motors, don't have alot of money in it, yet.
 
Confirm that the ignition is ok (good spark at both cylinders), but your symptoms could also be indicative of a gasket leak (have seen this before many times).

After you have checked your ignition I would take a good look at the carb gasket (why not replace it anyhow, it's super cheap) but I would lean a little more towards a bad powerhead base gasket.

A toasted base gasket often causes a miss or a sneeze, plus extra "smoke" or "steam", and generally "crappy" running/difficult start.

And yes, the base gaskets do go somewhat regularly on "portable" (6 thru 25 horse) Mercs that have been sitting for a while. On average I replace one or two a year...
 
galamb said:
Confirm that the ignition is ok (good spark at both cylinders), but your symptoms could also be indicative of a gasket leak (have seen this before many times).

After you have checked your ignition I would take a good look at the carb gasket (why not replace it anyhow, it's super cheap) but I would lean a little more towards a bad powerhead base gasket.

A toasted base gasket often causes a miss or a sneeze, plus extra "smoke" or "steam", and generally "crappy" running/difficult start.

And yes, the base gaskets do go somewhat regularly on "portable" (6 thru 25 horse) Mercs that have been sitting for a while. On average I replace one or two a year...
Click to expand...


Thanks, carb. gasket is new never checked base gasket.
 
Checked the kill switch, ok. New switchbox, new coils. No spark. I just have a standard multimeter and don't know how to make sense of the readings for stator check. Gettin cranky. Pulled the flywheel nothing looked cracked, melted, loose. Checked all ground connections. When cranking fuel flowing thru filter. I'm checking the spark with a spark checker it worked on the lawnmower wanted to make sure it was working. Not a bad mechanic but this outboard is killing me.
 
You need a DVA to check the voltages on the stator and trigger but you can do a simple ohms test on them. If you have continuity (very very minimal resistance) between the two stator leads and between the two trigger leads then at least you know the bobbins are ok enough that they should be producing power.

A secondary check is between each of the individual wires from the stator and trigger and a good ground spot on the engine block. Test each one at a time against the block - you should have zero continuity - if you have any kind of connection there then that component is grounding out (= no spark).

If you still have the flywheel off make sure the magnets are still in place - without them, no power.

If your ohms tests are good, and the magnets are there, try completely disconnecting the kill circuit (if you didn't last check). Simply pull the black/yellow wire from the bullet connector at the switch box and leave it unhooked - then check for spark.
 
Awesome, I will run those tests. Magnets are good. I did pull the kill circuit and still had no spark. I'll have to try in the morning, looks like rain soon. Thanks I'll let you know what I find.
 
Ok, ran the tests:
Trigger:
brn/wht to grnd = 155
brn/yl to grnd = 0
both together = .8

Stator:
blk/wht to grnd = .3
blk/yl to grnd = 95
both together = 104

Hope this makes sense. When I ran same with my continuity tester, I got none on any of them.

Thanks, Barry
 
Should have mentioned above you can try the "secret blow dryer test".

If a bobbin winding is cracked it may work fine when it's cold/cool but as the motor heats up, the copper expands and you have a disconnect.

The resistance between your two stator leads blk/wht and blk/yel looks a little high for a cold engine.

With the wires disconnected from the switch box, connect your ohm meter leads to each of the wires and then take a blow dryer (or a heat gun) to the flywheel and start heating it up.

If you all of a sudden lose continuity you have a breech in the wiring of the bobbin itself.

That "could" explain your symptoms - motor heats up, copper wire expands, loses connectivity = wont start - cools down a bit - copper shrinks regaining connectivity = motor starts...

Something else to try...
 
Hey thanks Graham! Replaced the stator and started right up!! Also replaced the trigger since it was the third time I pulled the flywheel. We've had so much rain this was the first chance I had to work on it. Probably should set the timing although it seems to be running very well. Will a regular old auto timing light work?

Thanks again Galamb and racerone - I did double check the kill switch circuit. And my better half says thanks, too.
 
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