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Thread: Yamaha 6hp 2 Stroke weird problem

  1. #1
    Join Date
    Aug 2009
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    Default Yamaha 6hp 2 Stroke weird problem

    This is a little beyond me.

    I have a Yamaha 6hp 2 stroke, 1999. Nice, starts great, bought it recently.

    It was not pumping water. I took apart the pump, everything looks great, impeller in great shape, etc. I have blown air through the the parts of the system I can blow air through and no problem there, upper and lower unit.

    After many take-downs and put-backs it started pumping water, but it took a long while to determine why:

    The shift rod has a small ring seal where it enters the lower unit. IF this seal is NOT IN PLACE, it pumps water just fine, but exhaust comes out of the hole for the shift rod.

    IF I put the seal back in place, effectively sealing off the lower unit to the atmosphere, it does NOT pump water I can feel hot air coming out of the telltale, so the impeller is spinning but no water.

    The through-prop exhaust conduit is not clogged.

    Obviously there is some air pressure problem here impeding water flow into the pump, but I cannot figure it out. I'm not a small-motor expert but can handle my own to a degree.

    Thoughts?
    Last edited by callsign222; 07-11-2017 at 04:02 PM.

  2. #2
    Join Date
    Mar 2007
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    East Quogue,NY
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    Default Re: Yamaha 6hp 2 Stroke weird problem

    First, ream out the tellale hole with a piece of 80-100 lb test monofilament fishing line. It's the perfect stiffness and diameter. If that is not available to you, strip the insulation from some Romex wire and use the stiff copper wire inside.

    Second: How is the thermostat? is it clean or clogged? Is it even in place?

    Try these two things.

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  3. #3
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    Default Re: Yamaha 6hp 2 Stroke weird problem

    But Kevin, it pumps water JUST FINE when I take the little gasket off the lower unit that's around the shift rod!

    I can do it while it's running... start it up, idle, no water, remove gasket around shift rod, boom, water starts pumping.

    Installed, never any water.

    Uninstalled, water.

  4. #4
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    Default Re: Yamaha 6hp 2 Stroke weird problem

    But Kevin, it pumps water JUST FINE when I take the little gasket off the lower unit that's around the shift rod!

    I can do it while it's running... start it up, idle, no water, remove gasket around shift rod, boom, water starts pumping.

    Installed, never any water.

    Uninstalled, water.

    It's gotta pump with the shift rod seal in place.May be some weird air pressure/ vacuum thing going on. In any event, I suggest you ream the passage; check the T-stat.

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  5. #5
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    Default Re: Yamaha 6hp 2 Stroke weird problem

    Here's a picture, water pumping. Red arrow points to the missing gasket, you can see it lacking from where the shift rod enters the lower unit (black ring is missing seal).


  6. #6
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    Default Re: Yamaha 6hp 2 Stroke weird problem

    Quote Originally Posted by Breakaway View Post
    It's gotta pump with the shift rod seal in place.May be some weird air pressure/ vacuum thing going on. In any event, I suggest you ream the passage; check the T-stat.

    Kevin
    OK, will do. I certainly agree with the air pressure/vacuum thing. Honestly I'm worried about the water jacket being full of something or other, corrosion, salt, whatever, impeding the pressure.

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