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  1. #1
    Like a chimp with a ball-peen hammer smackwave's Avatar
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    Problem after last round of mods

    Last night was my first chance to test my GPR aftere the last round of mods, and after 1/3 throttle the ski just falls flat on its face. No shut down, it just revs up to about 4500 RPMs then bogs badly. After limping home I took compression and got 148/150/130, so it looks like I'm in for at least one new piston on a fairly fresh GroupK 1390. Any thoughts on likely suspects while I'm tearing it apart? Last round of mods were:

    - Fercho VForce III reeds w/stuffer and spacer, I had to remove quite a bit of material from the stuffers to match the intake manifold
    - Relocated air/fuel separator to lower location in hull, but still have an uphill path on the pulse line (the fuel pump and air separator actually ended up on the bottom of my hull after a big wave jump on my previous ride, but were still working fine)
    - Turned low end screw 1/8 turn in to 1 turn out
    - Made new rubber gasket for flow control kit
    - Finally got rid of the bilge strainer (pump siphon is long gone) and connected water exit line from the stinger end directly to the bilge siphon exit
    - Replaced broken hi speed T-handle adjuster on middle carb and returned to 1 1/4 turn out

    Yeah, I commited the cardinal sin and did too much at once. Other engine related mods are:

    - GroupK 1390
    - Advent T3 CDI on Yam 84 curve
    - Accel pump removed, choke removed with primer, Prok arrestors
    - D-plate, free flow, Jetworks flow control

    I'm out of town this weekend, and I'll start the teardown as soon as I get back on Sunday. I'm keeping my fingers crossed that I can find the problem quickly, because the weather's too nice now to be working on the ski instead of riding it!


  2. #2
    Hydrotoys's Avatar
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    Did you pressure test the engine?

  3. #3
    Are we suppose to match the stuffers up to the intake? Didnt read anything about removing any material.

  4. #4
    r33pwrd's Avatar
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    with my set of VF3's it had a drawing showing what material to remove

  5. #5
    MPower's Avatar
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    Check your vacuum hoses from the carbs going to each cylinder. Sounds similiar to a problem I had, worth a shot.

  6. #6
    txgp1300r's Avatar
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    hey r33pwrd can you post that drawing..please

  7. #7
    Moderator RX951's Avatar
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    http://www.greenhulk.net/yamaha/view...0582f90f2c4bda


    Has your head been milled?

    please read the thread above........just another thing to look at........

  8. #8
    Like a chimp with a ball-peen hammer smackwave's Avatar
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    I was in a rush and did not pressure check the engine after installing the reeds. That'll definitely be part of the checkout to see what could have gone wrong. With the air/fuel separator there's only one fuel pump and pulse line anymore, and I plan on replacing the pulse line and some of the fuel line as a precaution and to simplify the fuel routing. However, the teardown will have to be delayed a bit because the missus broke her arm during volleyball playoffs and if I value my... erm.. life... I better be on hand to help out for a bit. Thanks for the advice guys!

  9. #9
    just GOT TO DO IT! great lakes gpr 1200's Avatar
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    harry told me NOT to do this: "Accel pump removed, choke removed with primer" said it would run lean.? loose signal vacume by doing it.
    Might be, may be not I'm interested to know. It's all that I see.

  10. #10
    Like a chimp with a ball-peen hammer smackwave's Avatar
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    Yeah, Harry didn't like it too much. He still put the jetting spot on for my carbs, though.

    Anyway, the verdict is in. There was an air leak on the #3 carb intake around the reed spacer plate. That cylinder is scored pretty badly (the crosshatching is barely visible) and will need to be replated. Tomorrow I''ll call Harry and see if he can swap cylinders and send me a new piston and ring set, and hopefully I can get it together and broke in by Memorial Day weekend for our beach trip.

    For now the stock reeds are going back on. I don't have time to make sure the Vforce reeds are completely fixed, and cylinders are expensive. It looks as if the cages stick out past the spacer plate (didn't know about that until too late), and I want to make sure my spacer and intake manifold sufaces are true before I reinstall them.

    On the stock reeds I'll need to replace some of the petals, since several of the sets are chipped on the rear corner of the rear petal. Does anyone know if the reed petals come in single or double sets (i.e will I need to buy one or two set per cage)?

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