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engine not going over 3500 rpm

Discussion in 'General Maintenance/Repair Questions' started by DVILLANDRE, Aug 9, 2020.

  1. DVILLANDRE

    DVILLANDRE Member

    32
    Apr 26, 2015
    long island
    1999 38" sundancer
    454 gas
    Both 7.4L mercruiser motors wont go above 3500 rpm. They were running fine 2 weeks ago, took the boat out today and they were very sluggish. Any ideas?
     
  2. sbw1

    sbw1 Well-Known Member

    Oct 10, 2006
    West Michigan
    This is listed in my signature
    This is listed in my signature
    IMG_5596.JPG Fouling on bottom of hull?
     
  3. Oh La La

    Oh La La Member

    66
    Sep 12, 2019
    400 Express
    7.4 MPI Horizons
    Dirty bottom
     
  4. DVILLANDRE

    DVILLANDRE Member

    32
    Apr 26, 2015
    long island
    1999 38" sundancer
    454 gas
    That's what I thought initially but we rode for quite some time it got a bit better but it seemed the engines weren't getting gas. At first we could only go 11 kts then it went up to 15 kts but they were definitely struggling.
     
  5. Oh La La

    Oh La La Member

    66
    Sep 12, 2019
    400 Express
    7.4 MPI Horizons
    It don’t take much growth on bottom and running gear to slow the boat down and 2 weeks in the summer can definitely do that.
    Especially with the hot weather we’ve been having!! Short haul, power wash and take it for a run, see the difference!!
     
  6. TUS NUA

    TUS NUA Member

    44
    Dec 4, 2019
    2003 320 Sundancer, Garmin GPSmaps 741xs
    350 Mercruisers (twin)
    Check spark plugs. Had the same issue on my starboard engine and it turned out that the spark plug in cylinder 8 was fouled. Changed them all and we are now running great.
     
  7. Snapon24

    Snapon24 Member

    90
    Sep 16, 2018
    Long Island, NY
    1988 340 Express Cruiser
    Twin FWC 7.4L Mercruisers w/straight drives
    What did you find? Bottom growth? I'm having the same problem now with mine except mine sat for 6 weeks.
     

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