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  1. #1
    Member BassinRN1's Avatar
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    May 2012
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    Pleasant Lake Mi.
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    Speed/RPM issues

    I have a 2017 Ranger Z521c with Mercury ProXS 250hp 2 stroke. No talons or PPs. Fully loaded this has always been a great boat. I could get 5850-5950 RPMs and run 68-70. Always been a bit relative to conditions of air and water temp as usual for most or all boat/motors. Currently running a Mercury Fury 24p 3 blade. Typically this has been the best overall prop for me and gave me the best numbers.
    But recently I can’t get close to those numbers. Been unable to get over 5600ish RPMs or 58ish mph.

    Any ideas.

    Thanks in advance.
    2017 Ranger Z521c (Blackout w/ Chrome Bullets)
    2020 Mercury ProXS 4 stroke 250hp
    MinnKota Ultrex 112 52"
    Humminbird Helix's (3 G4N Megas)
    Garmin 106sv Ultra with LiveScope and perspective mode
    Mark Peiser Manufacturing mounts (console and bow)
    Trickstep

  2. Ranger Boats Moderator jc2bg's Avatar
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    #2
    Dropping 10+ mph, I’d usually guess a prop issue or an engine issue. More likely the latter. Have you checked the plugs to see whether all cylinders are firing well? Do you have a hot foot, and if so, has the throttle setting slipped? The boat probably hasn’t gotten any heavier or less hydro-dynamic, so posting in the Mercury engines forum would also be a good idea. You didn’t say anything about the engine running rough, but if it did, possibly a bad batch of gas? If you’ve lost enough speed so that the boat isn’t fully getting up on pad, that’s one of the few ways that you could lose “only” 200-250 rpms and lose 10+ mph.
    John Clark — Findlay, Ohio

  3. Member BassinRN1's Avatar
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    #3
    Quote Originally Posted by jc2bg View Post
    Dropping 10+ mph, I’d usually guess a prop issue or an engine issue. More likely the latter. Have you checked the plugs to see whether all cylinders are firing well? Do you have a hot foot, and if so, has the throttle setting slipped? The boat probably hasn’t gotten any heavier or less hydro-dynamic, so posting in the Mercury engines forum would also be a good idea. You didn’t say anything about the engine running rough, but if it did, possibly a bad batch of gas? If you’ve lost enough speed so that the boat isn’t fully getting up on pad, that’s one of the few ways that you could lose “only” 200-250 rpms and lose 10+ mph.
    Thanks. I will post in mercury motors section also.
    Motor “runs” fine. Gets up on plane as well as ever. Just a speed/rpm issue. Doesn’t sound like it’s a motor issue as far as cylinders or plugs or anything. Sounds like usual when I have always ran it with no issues.
    Thinking it’s a prop issue but is same pitch I’ve always used but is a different prop. But is in very very good condition. No gouges dings or dents. So unless it’s just a flawed prop then m not sure it is a prop but I will be looking at getting another to see.
    Just trying to get thoughts on why this is happening.
    Thanks.
    2017 Ranger Z521c (Blackout w/ Chrome Bullets)
    2020 Mercury ProXS 4 stroke 250hp
    MinnKota Ultrex 112 52"
    Humminbird Helix's (3 G4N Megas)
    Garmin 106sv Ultra with LiveScope and perspective mode
    Mark Peiser Manufacturing mounts (console and bow)
    Trickstep

  4. Ranger Boats Moderator jc2bg's Avatar
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    Findlay, Ohio
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    12,932
    #4
    Hmmm. Well, there are flawed props. Also props that otherwise look fine but the cup has been reduced, either through well-intentioned tinkering or through wear, so that they don’t provide necessary bow lift. The only sure way to tell is to test with a *known good* prop, or have a prop expert like Mark Croxton spec out the prop for you.
    John Clark — Findlay, Ohio

  5. Member BassinRN1's Avatar
    Join Date
    May 2012
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    Pleasant Lake Mi.
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    #5
    Quote Originally Posted by jc2bg View Post
    Hmmm. Well, there are flawed props. Also props that otherwise look fine but the cup has been reduced, either through well-intentioned tinkering or through wear, so that they don’t provide necessary bow lift. The only sure way to tell is to test with a *known good* prop, or have a prop expert like Mark Croxton spec out the prop for you.
    Thanks. Great help
    2017 Ranger Z521c (Blackout w/ Chrome Bullets)
    2020 Mercury ProXS 4 stroke 250hp
    MinnKota Ultrex 112 52"
    Humminbird Helix's (3 G4N Megas)
    Garmin 106sv Ultra with LiveScope and perspective mode
    Mark Peiser Manufacturing mounts (console and bow)
    Trickstep