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  1. #1
    Seaman Apprentice
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    Default 2001 Mercury 125 runs on 2 or 4 cylinders?

    We just bought a 2001 Fisher pontoon with a 2001 Mercury 125 on it. I haven't gotten the motor model number yet but I do have a question. The gentleman that I bought the boat from said that at certain RPMs that the outboard would run on 2 cylinders and if you move it up a little it kicks in and would run on all 4. I have only had the chance to get it out once so far but there is a certain RPM range, around 2500 that it runs very smooth and at a nice slower pace. Then if I move the throttle just a very little bit the RPM jumps up to about 3000 and it feels like the other 2 cylinders do kick in and it really picks up power and speed. I have never owned a Mercury motor before and can't seem to find any thing on here about this feature ( if it really is a feature) so is this correct or is there possibly some thing wrong? The boat will cruise very nicely at 3800 to 4000 RPMs and will top out at just under 5000. According to what I found in an online manual the operating range for this motor is from 4750 to 5200 so this seems about right to me. I have also found that there is some water in both of the tubes to add extra weight so once that is resolved I expect to maybe run a little faster, correct?

  2. #2
    Fleet Admiral Texasmark's Avatar
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    Dec 2005
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    9,395

    Default Re: 2001 Mercury 125 runs on 2 or 4 cylinders?

    The newer model inline 4 cyl. engines which are mid hp engines (100, 115, and 125) do have a disabling feature for slow speed operation. I'm sure Merc had their reasons for the design but I personally have a problem with it as I like smooth trolling speed operation. That was one of the things I liked about the brand and that was they always had a lot of cylinders to keep things smooth. But mechanics on here have said that a properly adjusted engine runs as smooth as a 4 cyl.......well I'd have to hear that to believe it. I had thought that if I ever upgraded from my 3 cyl 90 to one of them I'd disable the function but it's not that easy as I have read up on it and there are some peculiarities with the engine in setting it up to run as it does that would complicate what I would want to do.

    So, not hearing your engine run, going from 2 to 4 at around 2500 rpm or thereabouts (Merc seems to like that number for several functions) is a normal function.

    Mark
    If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

  3. #3
    Petty Officer 1st Class
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    Aug 2011
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    Texas, the new Dust Bowl
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    277

    Default Re: 2001 Mercury 125 runs on 2 or 4 cylinders?

    The motors don't have idle circuits on the lower two carbs. The bottom cylinders come in, via airflow over the main nozzel and an accelerator pump. This typicaly happens between 1800 and 2200 or around 1/4 throttle on a properly set up motor.

    The Motors, when set up right, are seamless and idle like a dream, when wrong they are a PIA.

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