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Old 06-03-2012, 08:38 AM
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Default What can cause the stator/charge coil to burn out?

Mine went out in 2010. After some intermittent rpm loss thru-out the season, I stopped getting spark in all cylinders. I replaced the stator, which gave me spark again, but i still had some intermittent rpm loss - 1,000rpm drop when running 4,000-5,000 rpm, but only after 20-30 minutes of operation. Once the rpm dropped, it would randomly jump back-up, run ok for a while, then drop back off. Pumping the primer bulb has no effect.

Started my motors last Sat in the driveway for the 1st time of the season. This one was a little rough start - seemed like one side didn't kick in for a little while, but it did after warming up and seemed to idle well.

Went to launch on Sunday, and it just would not start. Checked it today - & I don't have spark again. Checked the Charge Coil, & I was getting a low voltage off it - 65v vs the recommended >175v. Ohms were low too - 395 vs the spec of 480 (+/- 50).

I will get another charge coil on there & see if that gets my spark back.

Is there another part of the ignition system that could be faulty and burning out the charge coil? I put a used one on for the last repair, so maybe it was just on its way out as well.

I also tested compression today, which looked good. Cold #'s were: 105, 105, 95, 105.
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Old 06-03-2012, 10:16 AM
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Twins? Having your battery switches on "both" will burn them out with both engines running. The charging circuits should not overlap anywhere in your electrical system.
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Old 06-03-2012, 10:30 AM
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They are twins. The only time I have had the switch on both is when i thought the starting battery was at risk of being low. I only have two batteries on now (planning to upgrade to 3 w/ the BEP cluster), and try to follow the #1 on the way out, #2 on the way in rule.

I didn't know having the switch on both would hit the charge coil. Thanks for the advice. The other engine has been running fine & showing none of the issues on this engine.
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Old 06-03-2012, 11:09 AM
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Stators have several windings in them.
Some power up the ignition, some provide charging current for the battery.
They are not connected in any way outside of being driven by the same set of magnets.

If you are having repeat failures on the same engine, a power pack may be causing a problem, its hard to isolate when they don't outright fail.
However they are connected, and rely on each other.

I had a pair of 150 mercs that popped on a regular basis, one after the other.
We ended up trying aftermarket stators because the OEM stators were unavailable.
They ran without problems after that, no further comment....
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Old 06-03-2012, 06:50 PM
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Interesting info, Rick - thanks. I would give a CDI stator a try, but will be repowering shortly & can't stomach the $250 cost.

I tried a different powerpack when I replaced the stator to see if the dropping rpm issue went away, but it made no difference.
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Old 06-03-2012, 07:29 PM
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Be sure the magnets on the flywheel arent touching the stator.
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Old 06-03-2012, 08:01 PM
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Heat kills them, and bad ignition coils will cause more heat.
You replaced with a used part instead of new, its a crap shoot.
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Old 06-04-2012, 07:35 PM
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I will double check the magnets. Agreed - used parts are a crapshoot, but I've got a retired OMC mechanic at the end of my street who hooks me up with parts at a price that is usually worth the gamble.
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Old 06-04-2012, 07:48 PM
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why would having dual batteries on twins running burn out the stators?
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Old 06-06-2012, 09:25 AM
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if the PORT engine charging system raises the battery voltage to a certain level, say 15.0 volts, and the STBD engine charging system is only producing 14.4 volts, then from the point of view of the STBD engine's charging system it is looking at an open circuit.
Current from the PORT engine's charging circuit would try to flow into the STBD engine charging circuit. Now, there are diodes which prevent this, but the effect of reverse biasing the diodes is to remove the load of the battery from the charging circuit. Then you are back to the forbidden case: operating the engine with no battery to absorb the charging current.

Basically the stronger charging system will burn out the weaker one
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