Please note this thread has been inactive for 90 days. For the best results, please start a new thread.
Results 1 to 3 of 3
  1. #1
    Seaman Apprentice
    Join Date
    Jun 2011

    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
    Join Date
    Dec 2005
    N. Texas, USA

    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.

    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
    Join Date
    Aug 2011
    Texas, the new Dust Bowl

    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.

Similar Threads

  1. Mercury 1989 45hp 4 cylinder runs on two cylinders
    By fozy64 in forum Mercury & Mariner Outboards
    Replies: 1
    Last Post: December 5th, 2010, 11:50 PM
  2. 2001 mercury 5.0 runs for 30 seconds then cuts out
    By regal987 in forum Mercruiser I/O & Inboard Engines & Outdrives
    Replies: 3
    Last Post: September 9th, 2010, 12:43 PM
  3. 2001 90 hp Johnson runs great for 5/10 min. then only runs 2800 rpm
    By ermess in forum Johnson & Evinrude Outboards
    Replies: 11
    Last Post: August 2nd, 2005, 07:25 PM
  4. 115 runs on 2 cylinders
    By ssschoeni in forum Johnson & Evinrude Outboards
    Replies: 8
    Last Post: August 12th, 2004, 07:20 PM
  5. 2001 mercury 60 bigfoot runs for a minute then dies
    By Localgrown 72 in forum Mercury & Mariner Outboards
    Replies: 1
    Last Post: July 28th, 2003, 09:10 AM
  1. iboats Forum Directory - Over 100,000 forum posts organized by topic