Inconsistent RPM's

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  • Captain Crunch
    Senior Member
    • Mar 2018
    • 30
    #1

    Inconsistent RPM's

    Hi All,

    Something that my motor has always done is have inconsistent RPM for any given day. Some days it will give me 2000 RPM at WOT, some days only 1700.

    The other day I had her up to 2250 RPM at WOT and cruised at 2000. This was after I gave the prop a good cleaning. This made me very happy.

    Does anyone else experience this?

    One thing I noticed was it will run at a lower RPM when I first motor out of the marina. I will shut it down and sail for a while. Start it back up and it will usually run better and give me a few more RPM.

    Just recently I actually heard the motor lose 150 or so RPM while cruising at 1900 or so. My alternator was not putting out and I thought it might have kicked in but this was not the case. It has since been replaced.

    Any ideas?

    CC.
    Tags: None
  • JOHN COOKSON
    Afourian MVP, Professor Emeritus
    • Nov 2008
    • 3501
    #2
    How long since the distributor advance has been serviced? Maybe it is sticking a bit.

    ex TRUE GRIT

    Comment

    • tenders
      Afourian MVP
      • May 2007
      • 1451
      #3
      How old is your tachometer? Mine seems to get a little sticky some days.

      Comment

      • Sam
        Afourian MVP
        • Apr 2010
        • 323
        #4
        I am also going to vote for the distributor advance lubrication check. I would also check for a little water at the BOTTOM of your fuel tank. Not sure of your set up but I would try to drain a gallon and see what you have.

        Comment

        • Captain Crunch
          Senior Member
          • Mar 2018
          • 30
          #5
          Thanks Guys.

          Water in Gas check is next on the list. Mech advance is good. I just went through it and have screwed around with the timing a bunch and seeing it smoothly advance just as it should.

          Maybe a symptom of a small intermittent vacuum leak in the carb or manifold spacer? Carb (4 bolt) was rebuilt and the manifold was taken off, cleaned up and reinstalled with new gasket. Surfaces looked good and I used a little sealant because the manifold side had some minor burn damage that 95% buffed out but I wanted to make sure I had a good seal. I have a PVC kit on it installed by the previous owner.

          Replacing the exhaust is coming up as well. I thought it might be related to changing exhaust back pressure from a failing exhaust system. I did have a serious overheating event.

          Motor seems to run really good now with impressive RPM's up to 2250 one day. I probably had a favorable current.... Definitely cruising at a reliable 1900-2000 rpm and making 5 knots+ in a Newport 30 fully loaded for cruising with a family of 4. A big improvement from the 4-4.3 knots and 1600 RPM I was getting previously.

          Sounds great, doesn't smell, no blow by.

          I'm now nit picking to get the best performance. I think with a clean bottom I could the boat up to a reliable 5.5 knots. If you would have told me that last year I would have said "not a chance!"

          Oh yeah...It's about to start charging a 265 Ahr battery bank.

          Thanks for everyone's advice, it has been much appreciated!

          CC

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