320 not producing enough power, sometimes

Discussion in 'General Discussion' started by jxm99, Apr 7, 2014.

  1. jxm99

    jxm99 New Member

    29
    Jan 27, 2011
    south florida
    320 Sundancer 2005
    twin 350 mag V drives
    So i took out my 320 yesterday for a cruise on biscayne bay. She started up fine and motored away from the dock just fine. When i went to get her up and going she wasn't producing enough power to get on plane. The RPM's never got over 3.8k at full throttle. I backed off and went again and i got a little more power and just enough to get her on plane using the trim tabs. I still wasn't getting over 36-3700 RPM's at WOT. Engine temp and all pressure gauges read fine just not enough power. By the end of the day, i was able to get both engines at full power and up to 4500 RPM's, not cruising at that speed just seeing what kind of power i could produce. Anyone have any guesses or ideas as to what may have caused this problem? I've have a few minor issues on the stb side engine. Is the boat smart enough to let the port engine know to not go full power if the other one isn't producing enough power?
     
  2. JimT

    JimT Well-Known Member SILVER Sponsor

    Jul 7, 2009
    Charlotte, NC- LKN
    2010 330 Sundancer
    T-350mags w/BIIIs & Axius, 5.0 kw Kohler
    When was the last time toy cleaned the running gear and the bottom?
     
  3. Celticknot

    Celticknot New Member

    95
    Aug 13, 2011
    Lake Erie
    05- 290 AJ
    V-drives - Genset
    350 mags
    Have you checked your strainers as well as the inlets on the bottom of the hull. Mine got plugged with weeds and I had the same problem you are describing. I took the inlet hose off in front of the seacock and had very little water flow.
     
  4. Dsybok

    Dsybok New Member

    388
    Jul 9, 2011
    Los Angeles/Lakewood, CA
    Currently Boatless
    Boatless
    What minor issues did you have with the stbd engine?

    I would look to bottom cleanliness first, its amazing what a filthy bottom will do to your top line performance.

    I had out of balance props at one point last year and they gave very similar symptoms to what you are describing. I could only make 14 kts and 3600 RPM tops. Balanced the props and 30 kts and 4700 RPM. No other change. Both my props were extremely out of balance. Did you hit anything recently that could have dinged your running gear?

    If your strainers were clogged I would think your motors would be overheating.
     
  5. jxm99

    jxm99 New Member

    29
    Jan 27, 2011
    south florida
    320 Sundancer 2005
    twin 350 mag V drives
    Bottom is clean, i just had the diver out 2 weeks ago. As far as the clogged filters, i don't believe that's the problem as my temp would've gone way up. It runs between 158-161.

    My issues were the starter and fuel pump. Nothing major
     
  6. dpmulvey

    dpmulvey New Member

    Dec 19, 2007
    Homeport: Charles City, VA
    1999/2007 330 Sundancer Hardtop.
    6.2 Merc Horixons
    1.5:1 Velvet Drives
    Bad fuel and/or filter clogged. If you are at a constant 4500 WOT, you are overpropped as well. You should be upwards of 5K.
     
  7. jason78

    jason78 Active Member TECHNICAL Contributor

    Sep 3, 2008
    Fort Mill, SC / Lake Wylie
    1997 20 Outrage
    200 Merc Offshore
    When is the last time you did a tune up? I have seen a bad cap and rotor cause this exact problem on several friend's boats. Cant hurt to do the plugs and wires too. But if they have not been done in a while I think you will find a new cap and rotor on each engine might be the fix. Good news is Mercury is back to using the "good" caps in their cap/rotor kit again. I don't personally recommend using automotive ignition parts on a boat for safety reasons but I am sure someone will chime in about that so it is up to you.
     
  8. jxm99

    jxm99 New Member

    29
    Jan 27, 2011
    south florida
    320 Sundancer 2005
    twin 350 mag V drives

    It's not an overprop issue. Boat was producing more power at WOT than earlier in the day but she wasn't giving 100%. I know that at WOT i should be getting closer to 5k rpm's
     
  9. Vince_nj1

    Vince_nj1 Active Member TECHNICAL Contributor

    Aug 25, 2008
    North Barnegat Bay
    2006 320 V-Drives 6.2s, Bow Thruster, Generator, Raymarine C80, Radar, Fish Finder
    6.2 Horizons 320HP
    My guess is your bottom, your shafts and your propellers are fouled. Even though you think your bottom is clean, I will bet that it isn't. I had almost the exact same results when I pulled my boat out at the end last year. My boat sat unused for 6 weeks. When I finally drove it to have it hauled for the winter it stuggled getting on plane. I could not get past 3500 RPM's and I was burning 40 gallons per hour at 19 knots. I immediately came off plane and trolled the rest of the way to the marina. The bottom didn't look that bad but my shafts were pretty fouled. It really is amazing how much drag bottom growth will put on a boat. My recommedation is to have your boat hauled and properly cleaned before you start tearing into your engines. It is highly unlikely that both engines have the same problem, the problem is your bottom.
     
  10. jxm99

    jxm99 New Member

    29
    Jan 27, 2011
    south florida
    320 Sundancer 2005
    twin 350 mag V drives
    i had that problem about 2 yrs ago where i thought she was clean but was pretty fouled up. this time i know it's good cause i have some underwater pics from the diver(which every diver should do). My mech is out ther and seems to think it's a spark plug/wire issue. I'll report back when i get some answers
     
  11. hack4alivin

    hack4alivin Active Member TECHNICAL Contributor

    Apr 18, 2008
    Joppa, Maryland
    320 Dancer
    Twin 350 V Drives
    I agree with Vince on this one, sounds like some type of bottom fouling problem. If your boat is equipped with Smartcraft, then your answer to the question “is the boat smart enough to detect a problem” is YES. But what it will do like in the case of mentioned above is go into throttle limit mode and the engine will not go above 1800 RPM’s. The Smartcraft system will detect low water flow on the raw water cooling side and limit the engine speed. Since you are reaching and sustaining 3800 you are not in throttle limit mode.

     
  12. Dsybok

    Dsybok New Member

    388
    Jul 9, 2011
    Los Angeles/Lakewood, CA
    Currently Boatless
    Boatless
    WOT On a 320 Dancer with 350s is 4950, anything over 4600 would be pretty good on a boat this age. I am happy when I see 4800.

    The fact that it started out slow in the beginning of the day makes me suspect bad props, dirty bottom or something else going on with the running gear as well. Maybe as the boat ran, the crap sloughed off and that is what caused it to get better. Or he was dragging some lines or netting some of which came loose later in the day.
     

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