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  1. #1

    MAJOR Yamaha HIDDEN defect

    I found a hidden factory defect that may explain why these motors are prone to lean fuel siezures, and I don't think it was just on my ski.

    I recently bought a 2000 yamaha 1200 xlt with the power valves. It has 3 mikuni super bn carbs. It was siezing I believe from lean fuel condition. Anyway, in the process of rebuilding the factory carbs, I put a 1/8" tube to my mouth and the accelerator fuel line (90 degree elbow) inlet nipples going into the mikuni super bn mag and pto carbs (the center carb does not have an inlet) to check if they were clear (its hard to tell when blowing compressed air with a large air nozzle). No air passed through. I removed the pressed in elbow by just pulling it out with pliers.

    1. I inserted a paperclip and discovered the larger tube was blocked for about 1/8" just before the turn in the elbow (the smaller tube was clear). The blockage was also smooth and evenly shaped like the crown of a piston. It was solid brass, and I think part of the molded elbow? I attempted to drill it through, but got off center and messed up the elbow. I was not able to use a punch to keep the drill bit centered. The drill shavings were defintitly brass.

    2. I also discovered that the smaller diameter extension tube that extends into the carb throat from the elbow was also blocked inside and the blockage is solid brass.

    3. After messing up the accelerator fuel elbow inlet, I have considered just using the injection oil carb throat inlet and switching to premix fuel. What do you think? Yamaha does not sell the elbows. You have to buy the entire carb!

    4. Have you seen this before? I wonder if Yamaha should do a recall and accept liability for all our siezed motors?????

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  2. #2
    WE DONT DIAL 911 RDH's Avatar
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    yes switch to premix!! get rid of that oil pump bull****..

    it might be a little harder to fill up on the water but its better than not being on the water...

    im gonna look at my carbs tonight and see if ive got the same thing..

  3. #3
    Hydrotoys's Avatar
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    Honestly RDH,
    You have a better chance of opening a "water and ice" store in Hell, than get Yamaha to broadly accept blame for a blocked accellerator pump nozzle.

    Of course there was those dropped power valves, snapped crank snouts, middle crank bearings, piston pins backing out, and probably a few things I forgot...

  4. #4
    All hail the Chief! fullboogie's Avatar
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    That's a major reason why most people remove the acc pump and rejet. Fercho has been preaching about this for years and years.

  5. #5
    WE DONT DIAL 911 RDH's Avatar
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    Quote Originally Posted by hydrotoys View Post
    Honestly RDH,
    You have a better chance of opening a "water and ice" store in Hell, than get Yamaha to broadly accept blame for a blocked accellerator pump nozzle.

    Of course there was those dropped power valves, snapped crank snouts, middle crank bearings, piston pins backing out, and probably a few things I forgot...

    yo hydrotoys i didnt start this thread.....

    i know yamaha wont do ****.



    hell could probably use a water and ice store though.

  6. #6
    steach's Avatar
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    Quote Originally Posted by RDH View Post
    hell could probably use a water and ice store though.

  7. #7
    Hydrotoys's Avatar
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    yo hydrotoys i didnt start this thread.....

    i know yamaha wont do ****.
    I plead sleep deprivation!

  8. #8
    WE DONT DIAL 911 RDH's Avatar
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    thats what they all say!!



    well we could sell bbq with the ice .... maybe we could get in tight with satan....

  9. #9

    reply

    Thanks folks, heres a reply and update I posted to pwctoday forum. I'm interested the the ball valve in 4th paragraph.

    Thanks for all the input. I should have put a question mark after the title of my post. Sorry. Maybe if Yamaha could make their service manuals half as detailed as a General Motors factory service vehicle manual I would not be in this mess.

    For the record, I never experienced a hesitation or stumble on acceleration. I had no symptoms to indicate accelerator pump malfunction other than my discovery of the blocked nipple.

    Hey Wedoseadoo, you said there was a ball valve in the carb inlet elbow nipple. That’s a good explanation, but when I tried to compress the undamaged one on the pto carb with a tiny punch, it would not budge. I also attempted to pressurize it with a Mikuni 100 pound pop off gage, but could not get the gage tube sealed tight enough over the elbow to hold pressure. I used two small zip ties, but still not tight enough. So my first question, how much pressure should it take to move that little ball?

    And my second dumb question, if the accelerator pump only puts out fuel during acceleration, what purpose does the ball valve serve? What would happen if there was no ball valve and, say, I just used an abandoned oil injection nipple which has no obstruction?

    Third question, what is the best way to disable the accelerator pump and what would I rejet the stock motor and carbs to? The stock jets are 117.5 high on all three carbs and 87.5 low on all three.

    Mag Center Pto

    Main -
    Pilot -


    Fourth question, what mixture needle settings would you recommend with your suggested jetting?

    Mag Center Pto

    High -
    Low -

    Again, sorry for the false alarm and thanks much for the help.

  10. #10
    Those nozzles get clogged all the damn time. Once really clogged you ussually cant get them clear.

    Although I'm a big fan of not running the accelerator pumps, you don't have to buy the whole carb body to replace the nozzle.

    Jetworks sells them, www.jetworks.net

    Also go through the rest of your carbs and make sure they arent gummed up.

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