1991 OMC cobra 3.0 2500rpm max under load

Discussion in 'Inboards' started by Billy the kid, May 31, 2014.

  1. Billy the kid
    Joined: May 2014
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    Location: North carolina

    Billy the kid New Member

    This is my first boat that i have ever worked on myself and I am still learning. I have a 91 3.0 liter omc I/O that I have recently acquired. The motor ran like hammered crap and I needed to do some work. I have since rebuilt the carb to spec, done tune up, plugs, wires, cap, rotor, ignition module, and coil. Now the engine starts smooth, shifts into forward and reverse great, and will rev out of water with the muffs on just fine. But when I get it into water, the engine will not allow me to go any faster than 5-10 mph or approx 2500rpm. I pulled the prop off the make sure the hub wasn't spun and was fine. I am at a complete loss now. Any suggestions will be helpful. Thanks a lot
     
  2. whitepointer23

    whitepointer23 Previous Member

    have you checked to see if you are getting full throttle. push it to the stops and go and have a look in the carby.
     
  3. Billy the kid
    Joined: May 2014
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    Location: North carolina

    Billy the kid New Member

    I probably should have mentioned that. Yes it does. When I move it to full in either direction, the butterflies open completely and it give it a big squirt of fuel in both barrels
     
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Which ignition module did you install? Did you install the heat sink under it? What's the voltage at the purple wire on the module? Do you have a good, clean ground?
     
  5. slow fred
    Joined: Feb 2011
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    Location: florida

    slow fred Junior Member

  6. Billy the kid
    Joined: May 2014
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    Location: North carolina

    Billy the kid New Member

    @par: I installed the same factory gm ignition module that omc calls for, I have 13.4-13.8v at the purple wire at the coil at idle. I do have a good ground. There is no heat sinc included or present at the distributor cap.
     
  7. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    How about the advance plate - got good movement/springs? Place a mark about 1.75" forward of the "0" mark on the harmonic dampener (where the timing marks are). This is about 30 degrees on your engine and where you should see the timing pointer at about 1,800 and above RPM. This is a quick way to see if your getting advanced properly.
     
  8. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    It does sound like spark advance, or possibly it is not firing on one cylinder.
     

  9. whitepointer23

    whitepointer23 Previous Member

    no worrys, it was just a thought . sometimes I kick myself when I don't check the basics like that first .
     
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