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97 25 hp mercury

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  • 97 25 hp mercury

    i just got this 97 mercury 25h it ran good for coupledays then i noticed the prop was spinning so i had a anouther 25 long shaft i took the prop and put it on my 97 short shaft. now the motor is running in very high rpms and not moving like it was before . could it be my lowerunit going badd

  • #2
    Re: 97 25 hp mercury

    3 vxv

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    • #3
      Re: 97 25 hp mercury

      Ok, just for clarification, you got the 97' 25hp and you had another 25hp long shaft? Was the 97' 25hp the short shaft or is that another motor? Sounds like you're talking about 3 motors but I don't think you meant it that way.

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      • #4
        Re: 97 25 hp mercury

        So you have two Merc 25's? A long and a short shaft? Sounds like you need to check the pitch on the prop you put on the motor. Lets say the one that was bad was a 13p, and the one you put on was a 11p...then 11p is going to cause your RPM's to be alot higher than when running the 13p....and you will lose speed. As of right now, it does not sound like your lower unit. The more pitch you have, the more water it pushes, the more torque it has on it, the slower it turns, and the faster (in some cases) the boat moves. The less pitch, the less water it pushes, the less torque it has on it, the faster it spins, the speed you lose (in some cases)

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        • #5
          Re: 97 25 hp mercury

          well i justed checked my pitch is the same on both props what about the hub behind that or even the oil in the lower unit

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          • #6
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            Re: 97 25 hp mercury

            If you havnt changed the lower unit oil in a long time, then by all means do it. It is possible to have two props with bad hubs. Usually hubs will give out, and cause the prop to "slip". Either they go all the way out and the hub moves and prop don't, or there is some level of slippage going on. You can take some white paint, or make a mark across the hub and the barrel and test run it. If you look at it after the run and the marks have moved....then you need to either re-hub your prop or get a new one. Also are both props from the same company? Both Stainless or Aluminum? Both have cupped or straight blabes, both progressive pitch or straight pitch? Little differences between companies change the way props cause motors to perform. Cupping on the blade may make rpm's drop, Progressive pitch will get you out the hole faster then a straight pitch. Aluminum has some flex where stainless don't. Even the diameter of the blades make a HUGE difference. If they are the same company, same pitch, same material and design.....and same condition then check the prop hubs.

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