BWP's Mercury, again.

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  • BWP's Mercury, again.

    It's now maxing out at 4600 not 5250 like it should, power is down as well, recently replaced switching and now possibly trigger is going out.
    Had a weak spark on number 1 and swapped out one from repair shop, no change in spark.
    Only tested 1 at a time on plug checker.
    It's take a lot of torque to get it over hump, after that It's only 46-4700 max, needs 5-500 more rpm to be correct. If I had 3 grand cash, I would place a large down on a new Mercury, SHOCKER!.
    Opinions welcome, just want to nurse this one along till money tree starts dropping.
    BWP

    $CASH.

  • #2
    Is it spark or fuel?
    Engine Sales and Service
    Ph +1 954.463.1515
    Fx +1
    954.463.4904
    Toll Free: 800.622.6747

    oparker@parkeryacht.com
    www.parkeryacht.com

    Member of the MSHS Group

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    • #3
      Not certain! My redneck tests say not fuel, am going to try a smaller pitch prop to rule out either, putting minimal money in till I have a down on what I really want.
      Boats, not the smartest thing to own, but much more fun!.
      BWP

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      • #4
        Why change props, wasn't it turning good rpm's last year with the current set up? Run it and kill the engine right after it messes up. Pull the plugs. Black means rich (not firing) White will be lean.

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        • #5
          Splashed it, had prop repitched to 15 from 17, rpm still maxed out at 4600 rpm, should be 52-5300.
          The smaller pitch helps it get on plane easier, but is merely a crutch and I'm fully aware of it.
          I think my 115 is now a 88.75 3 cylinder, I Don't care, not likely going to put much more cash in this money pig!
          Definitely not getting full performance out of it as, it is what it is. Gets me to the sandbar and back, fishing is for other people's boats!
          Yes, I'm willing to accept mediocre performance as It's all I can afford for now!
          150 Mercury one day!
          I'm not smart, but I'm good!.
          BWP

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          • #6
            It doesn't cost anything to determine what the cause may be, and running it with what's a minor problem now, could destroy the motor.

            Check for spark on each plug.

            Pull each plug wire off one at a time while it's running, it should run worse each time, if there's no change you found the problem cylinder.

            Check compression.

            Try hitting the choke and see if it improves or gets worse.

            Squirt some pre-mix into each carb when it's running at high RPMs to see if it gets better.

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            • #7
              As Ondarvr says, running lean may kill it.
              Tinker a bit. You like to tinker? Right?

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              • #8
                Yeah what he said Especially if its premix...Charlie

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                • #9
                  Did Mercury make test props for their motors?

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                  • #10
                    Originally posted by ondarvr View Post
                    It doesn't cost anything to determine what the cause may be, and running it with what's a minor problem now, could destroy the motor.

                    Check for spark on each plug.

                    Pull each plug wire off one at a time while it's running, it should run worse each time, if there's no change you found the problem cylinder.

                    Check compression.

                    Try hitting the choke and see if it improves or gets worse.

                    Squirt some pre-mix into each carb when it's running at high RPMs to see if it gets better.
                    It may just be a clogged high speed jet. Like ONDARVR said 1: Figure out which cylinder 2: Determine fire/spark, compression, or fuel. Go from there, don't kill it over something minor.

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                    • #11
                      Thanks for all input guys: Well, just ran the boat again, ran just like before, no change.
                      Disconnect no.1 spark plug lead, started up, idled like before, way to low!
                      Accelerated to the same level of performance as before! 4600 max It's very strong, even as a 3 cylinder 88.75 hp outboard.
                      so-----no.1 is not firing!
                      Switchbox replaced 3 months ago with new one, coil exchanged with one from shop.
                      question, is it the trigger assembly?
                      except for missing it runs fairly well with a lower pitch prop and still gets on plane fairly well as a 3 cylinder.
                      This Mercury 4 cylinder is referred to as a 2+2 model, it idles on top two till 1800-2000 rpm when speed is enough to pull fuel through high speed jets, it has no idle jets on bottom two!
                      Weird Mercury design at the time.
                      It now idles horribly as 1 cylinder is pulling 3 cylinders until accelerator pump kicks in and it jumps, no smooth transition, all or nothing.
                      Very irrating!
                      My 2 speeds are stalls out or jumps on plane, not good for no wake zones.
                      Trigger assembly is all that's left, if It's not too much, I'll get one, if not, I'll run till it blows.
                      It runs great at 3800-4600, not so well below that, that's my dilemma.
                      Even 3 cylinder 2 strokes have torque, this 115 continues to impress me, 88.75 horsepower and all.
                      Comments please! God bless America!
                      BWP

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                      • #12
                        Tested again in barrell, same results, not firing on no 1.
                        While idling safely pulled no 2, stopped immediately!
                        Remember, bottom 2 fire above 1800 rpm, no idle jets!
                        So when it is idling no 2 is carrying 3 cylinders, that's a tough life!
                        When on water as soon as rpm gets above 2 grand, hold on, it blasts off!
                        Is this my trigger assembly going bad?
                        Sure runs better When it runs on all 4, and more fun too!
                        HELP!!!!
                        THANKS!!!
                        BWP

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                        • #13
                          Spoke to Mercury shop, trigger assembly is under $140.00, guess that is the next most likely step.
                          Wish me luck.
                          BWP

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                          • #14
                            Wish I could help but I don't even know what a "trigger assembly" is.

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                            • #15
                              Mercury's term, it receives voltage from stator, sends it to Switchbox then triggers it as to when to fire each cylinder.
                              To each coil.
                              Other's understanding ignition systems better than me should be able to expand on my rudimentary knowledge.
                              My writing this does not mean I fully understand this topic.
                              Just want my Mercury to develop full power and bring fun back to my boating.
                              Thanks,
                              BWP

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