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Potential Tachometer Issue 2007 Nitro 189 Sport 150 Optimax

Thread in 'Motors & Props' started by Kswan, May 6, 2019.

  1. Kswan

    Kswan New Member

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    Hello
    I recently purchased a used 2007 Nitro 189 Sport with a Mercury 150 Optimax.

    I'm seeing about 56mph with 1/2 tank gas and only me in the boat. It has 21p Laser II prop. The issue is my Tachometer is reading 6400+ rpm. I believe the motor has an over rev alarm but have not heard it. The max RPM for the motor is 5750.
    Also I can have it trimmed all the way down and still exceed the 5750 rpm. Runs about 6000 when WOT and trimmed down.

    Is it the Tachometer that's misreading or wrong prop pitch?

    What do other people see for top end on a similar setup?

    Thanks
     
  2. Thomas Teller

    Thomas Teller Member

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    Check your motor manufacturers recommendation. It sounds like you are over-revving, the prop is slipping in the water. You could damage the motor, be careful.
     
  3. jerry shack

    jerry shack Well-Known Member

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    How's the hole shot ? That Laser II is about bow lift and that 150 Opti will give you a alarm when over revved no revlimiter. If your system check is working correctly, that's the alarm when you turn on the key on. If no alarm when you turn on the key you got a problem. If the hole shot is outrageous possibly to small of a prop. However another tach should be tried first(that's the cheapest) or you can go to a dealer and get your PCM (Propulsion Control Module) scanned it will tell you all the RPM's and how long they where, also how many recommended over RPM's was reached. And a fault codes present.
     
  4. Kswan

    Kswan New Member

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    The hole shot is actually fairly slow. I brought the boat into a mercury service shop and had the hours checked and Tach looked at. The hour report showed no over revving ever and they were able to reset the Tach and now is reading much closer. I'm seeing about 5600rpm at WOT.

    Thanks for the info. though
     
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