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07-12-2020, 02:33 PM #1Junior Member
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'87 Mercury 115, running poorly in gear only
Hey Folks,
I know OMC crossflows like the back of my hand, but I'm new to Mercury. I'm helping a buddy out.
Okay, so, Merc 115 inline six, 2 stroke, carburated, 1987.
Starts, idles fine, can even rev out in neutral in the water. But, as soon as I put it in gear, stutters, sputters, and can't build rpm.
Fuel pump has pressure, checked the plug wires with my timing light, replaced a damaged coil pack, they all seem fine.
The problem started on the water. Boat was running fine. Shut it down, hung out, and fired it back up after a while and ran like crap in gear.
Lower end trouble? High speed jets? Electrical? Get me started on something?
Thanks again,
The Last One
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07-12-2020, 06:04 PM #2Scream And Fly VIP
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How's the compression for the motor? It sounds familiar to me.............with my own motor. You may find low compression is the culprit.
High speed jets wouldnt affect the low speed "in gear".
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07-12-2020, 09:55 PM #3
stator.
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07-14-2020, 06:36 PM #4Junior Member
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Update!
So, I checked compression. It was good on all cylinders 92-98 psi. I couldn't check cylinder six because it was too low in the cowl to get my gauge in there, but it's likely good given the others are fine.
Checked coil packs. Each reads 0.92 - 0.98 ohms, except one which I just replaced and reads 1.41 ohms.
So, now I'm pulling the carbs to clean jets.
Capt. Insane-o, how do I check the stator?
Thanks again,
TLO
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07-14-2020, 06:42 PM #5Screaming And Flying!
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Good strong battery, carbs open, 3-4 pumps to 92 psi?
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07-14-2020, 08:07 PM #6Junior Member
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07-14-2020, 08:22 PM #7
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07-14-2020, 08:37 PM #8Junior Member
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SS170: I have a digital voltmeter.
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07-14-2020, 10:16 PM #9Screaming And Flying!
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Probably covers everything
http://www.cdielectronics.com/wp-adm...S-174-5456.pdf
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07-14-2020, 11:21 PM #10
If thats a reptuble compression gauge they won't run on 98 psi. The bores are tapered and it will fall on it's face at throttle pick up.
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keefallan liked this post
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07-15-2020, 03:23 AM #116000 RPM
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Idle set out of water. Seen it done many times.
plus the other stuff.
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07-15-2020, 07:13 AM #12Junior Member
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Hmm, guess I'll recheck compression with WOT.
But they're all real close to eachother, so I doubt that it.
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07-15-2020, 07:25 AM #13Screaming And Flying!
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Yeah, 6 beautiful consistent tried bores. Great motor though, fix it right whatever it is. Hoping it's just hose tuned as mentioned above.
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07-15-2020, 08:03 AM #14
I'd still lean toward the stator (low speed windings). Running fine, shutting down, then runs like crap seems more like ignition. A DVA tester is an adapter that plugs into your Fluke, it measures peak voltage for that split second that a meter alone cannot read. Try and find one and follow the CDI troubleshooting guide. You will then be sure if it has anything to do with ignition.
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07-15-2020, 09:06 AM #15Screaming And Flying!
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What boat is it on? I mean worst case you needed to do the bores you could work some magic for some gains. Many say just leave it stock and that's true but that's not the only way.
These folks were highly recommend by a pure inline guru for their machining , if you need it .
http://www.wintechenginemachine.com/index.htm
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