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Df140 2006 missfire /hunting up and down

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  • Df140 2006 missfire /hunting up and down

    Hi all,

    i have a pair of df140s 2006, haven’t used the boat in a few months but start and warm up every couple of weeks.

    went to use it this weekend and the port outboard had a bit of a cough splutter when it started but seemed to idle ok, maybe a little bit rough.

    once in open water, boat would start to plane around 2500-2600 rpm and after 5 or so minutes start to sound like a misfire under load, but hunt up and down by about 100-200 rpm. Didn’t like trying to push past 3000rpm but I was in an 8 knot zone the entire time so didn’t try any high speed runs.

    pulled plugs and all look good, have the alloy **** plug fitted and had zero corrosion around that area when I installed a year or so ago.

    checked external fuel sep for water but no water.

    tomorrow I’ll check the neutral start switch, as I had that fail last year on the other df140, can’t remember the symptom though.

    Anyone experienced this? Best part is I have two side by side so swapping parts to fault is quite easy

  • #2
    Are both engines running rough or only the port engine?


    • #3
      Only port engine running rough, last night I inspected the neutral start switch and drained the vst fuel was clean no water and NSS looks to be ok.
      Last edited by johnnyt81; 12-23-2020, 05:30 PM.


      • #4
        Neutral throttle switch, NTS, if failed will prevent the engine revving past about 3000rpm. And will be doughy from idle up to 3000 as well. At 3000 it will be like a race car hitting the pit lane limiter, it will be bucking and misfiring because spark and fuel deliver is being interrupted by the ecu.

        Running rough is unlikely to be NTS.

        If its close to due for annual service, why not just do that including put in a new set of plugs.


        • #5
          Installed new plugs, drained vst, filled with fresh fuel swapped coils to other outboard in case the problem followed them. Went for a run and both outboards worked perfectly.

          my guess is plugs were breaking down under load.