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RPM fluctuation at low speed - twin F150

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  • RPM fluctuation at low speed - twin F150

    Good Morning,
    Last week, I was out cruising the ICW as I haven't been out in a month or so due to weather, work, etc. On my way back to the ramp I noticed my port motor (I have twin Yamaha 2012 F150 4 strokes with approx. 590 hrs.) rpm's started to fluctuate without any movement of the throttle. The rpm's were at 1300 then dropped to btw 1000-1100, then down to 700-800 to then back up to 1300. I started to get worried so I gave the engine gas/throttle and it held fine at 1500 and 1700 rpms. This happened a few times on the way back until I reached the ramp (but noticed it was only at that current RPM of 1200-1300). At the ramp, when putting the boat on the trailer and just in gear there were no issues. I have asked several friends, other Yamaha owners, etc. and have heard things such as the primer ball, fuel water separator or the TPS. I haven't had a chance to look into yet but will soon. I was wondering if anyone has experienced this issue and/or has any idea to what it may be.

  • #2
    take off your fuel water separators, dump them out (pour the gas into your truck or lawnmower) refill them with clean gas and a splash of seafoam or ring-free, put them back on (better yet replace them - and fill the new ones with clean gas they aren't expensive). If that solves the problem then you may have some watery fuel.

    If it doesn't, we can dive deeper.

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    • #3
      Originally posted by JerEazy2 View Post
      take off your fuel water separators, dump them out (pour the gas into your truck or lawnmower) refill them with clean gas and a splash of seafoam or ring-free, put them back on (better yet replace them - and fill the new ones with clean gas they aren't expensive). If that solves the problem then you may have some watery fuel.

      If it doesn't, we can dive deeper.
      I will give that a try - appreciated the response.

      Comment


      • #4
        You should have an engine fuel / water separator under the hood. It faces forward. Yank the hood inspect (and or dump)..

        The clear cup (more yellowish):

        That red ring, if there's water inside, will float.

        I believe your newer engine has a sensor (and wires) in that cup that detects water.


        Last edited by TownsendsFJR1300; 02-23-2018, 01:26 PM.
        Scott
        1997 Angler 204, Center Console powered by a 2006 Yamaha F150TXR

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        • #5
          Originally posted by TownsendsFJR1300 View Post
          You should have an engine fuel / water separator under the hood. It faces forward. Yank the hood inspect (and or dump)..

          The clear cup (more yellowish):

          That red ring, if there's water inside, will float.

          I believe your newer engine has a sensor (and wires) in that cup that detects water.


          Question: would an alarm have gone off? I am going to take a look at this as soon as I get home. thanks for your response

          Comment


          • #6
            Originally posted by RobD1220 View Post

            Question: would an alarm have gone off?
            when present and working correctly, water in that filter, tripping the water-in-fuel switch, causes the keyswitch warning horn to sound - but only when in neutral.

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