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Posts: 430
| 2012 Merc 90 hp 4 stroke.
So couple weeks ago motor seemed to idle rough and felt like a misfire at lower speeds but accelerated fine and ran fine at top speed. Added fresh fuel and some seafoam ran good next day.
fast forward two weeks and noticed rough idle every once in a while.
Also noted that the last bunch f trips took longer to start different times of the day.
Never had plugs changed!
Suggestions to get through rest of season? Bad plugs? Bad gas?
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Posts: 771
Location: Delavan, WI | I would replace plugs, easy cheap and should be done regularly anyways id say they're definitely due 7 years later. I had a 2000 Mercury 2 stroke that would start bogging and hesitating at lower rpms every other year, put new plugs in it and ran great again for a while. Looking at plugs they always looked ok but sure made a difference, so that's where I would start. Could also be carburetor related but for sure throw some plugs in anyways and run it wide open and hard for a bit after fully warmed up and then see how it is
Edited by muskymartin67 9/22/2019 11:49 AM
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Posts: 1670
| Fuel filter. |
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Posts: 3472
Location: Elk River, Minnesota | Hiya!!
I'm thinking both responses are spot on. Since the motor is at least running, I would run some straight decarbonizer into the throttle body throats after the engine is warm. Set it at high idle (1500 RPM's or so), then start spraying into the throats with either pressurized seafoam or mercury powertune. The motor will start to sputter a bit and blow white smoke but keep doing it for a couple of minutes. After that, and if you can physically get it done, spray continually into the throats to kill the engine. After it kills (or you manually shut off), spray more into the throats for a bit, then let the engine sit for 30 minutes or so to let the decarbonizer really dig into any carbon build up. After sitting, start it up and take it for a drive...get it up to speed to clean all the gunk out through exhaust. Be prepared, though...there is a possibility that with plugs of age in there, one could easily foul out going through this process, so having an extra plug or two along might be a good idea for a quick on-the-water replacement.
Second, replace the plugs and fuel filters. If you have a fuel/water separator on the rig as well, remove, empty and replace the filter, and let the fuel sit in a clear glass jar just see if there is anything foreign that might have gotten in. The engine most likely has some sort of filter on it as well that, if for just peace of mind, replace it as well.
If the plugs have never been replaced, they are most likely not within spec for gap, and for their age, I'd say well over time to be replaced. Not sure of the type of plugs the engine uses, but if they run $3.00 or so per plug as many of the older, earlier carbed engines/two strokes had in the past, it is also peace of mind to replace yearly as well after spring start up and clean out of any fogging oil that may have been used.
Steve
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Posts: 410
Location: With my son on the water | I had a very very similar issue with my merc 150. I called the merc technical info center and the person I talked to recommended simply adding merc Quickleen to the gas to clean things up (carbon). He said start with the amount recommended on the bottle, run it, let it soak, and run it again. He said increase the concentration until things clear up and it runs normal. That’s what I did and it was so easy, cheap, and worked great. Now I do that every spring to remove the stabilizer spray.
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Posts: 3472
Location: Elk River, Minnesota | Juhas,
Any udpdates with your motor?
Steve |
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Posts: 1209
| My motor started skipping some and within an hour of use was very bad. New plugs and all better |
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