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Yamaha 250 Prop Question

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  • Yamaha 250 Prop Question

    I have a 19inch prop on my 1996 Yamaha 250 pushing my 1977 25cc. I am unable to get rpm's above 5k fully loaded which puts my cruise at about 28mph at 4500. Is this a prop issue or is this fairly standard??
    Rooster[br]1977 25CC[br]New Orleans, La[br][br]

  • #2
    What's the max RPM that motor is supposed to turn? Sounds like the boat may have gained some weight [water in foam] or a little to much pitch.


    • #3
      Hey rooster I have a 1984 254 with a 1997 Yamaha and I cruise at 25-28 mph at 3700 rpm with fuel fuel 151 gallons I'll check my prop and get back to you tommorrow


      • #4
        In order for the motor to perform properly (according to the factory power curve) you need to have the motor RPM's in the range that the factory has set up for WOT for that specific motor. Most motors are rated for between 5400 to 6000 RPM's WOT. If you motor is not running in it's recommended RPM range with a fully loaded boat then you need to either lighten the boat OR change the pitch on your prop. If your not getting the RPM's you should be, then the pitch of the prop needs to go down - probably by 1 or 2 pitches. That, however, needs to be tried on the boat, as there is no specific formula for exact prop size. Most standard props all come with the same diameter but go up (or down ) by 2 pitch for each of the sizes (i.e. - 15"x17 or 15"x19 or 15"x21 etc.). If your convienced that a change of 1 pitch will do the trick, then find a local prop rebuilder (your local marina will know who in your area does this) and ask them to change the prop by one pitch. Also, sometimes you can fool with the diameter of the prop - sometimes going to a smaller diameter with more pitch will also raise the RPM's. But for the first pass try the pitch. Also, if you ARE NOT using a Stainless Steel prop do yourself a favor and get one as the thiner blades will give you more performance because of the thiner blades and the cupping on the blades. It will, however, cost more that an Aluminum - say $400 to $500 but is well worth it. Then use the Al prop for a get home spare. Hope this helps -

        1973 22 CC Milford, CT USA[br]