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  1. #1

    1998 GP 1200 compression question

    Hi boys, my first post here

    I'm from italy...

    I'm considering to buy an used waverunner gp 1200. It is in very good conditions and had on the engine only 124 hours.

    The only "damaged" part is one air filter.

    Tomorrow I'm going to test it in the water but before I want to do a compression test to understand the global state of the engine...

    I've seen various videos that shows values between 115 and 120 PSI....Can you write me a correct list of values related to the cylinder state?

    For example

    130 PSI: Perfect...
    120 PSI: good
    100 PSI: too low, stay away...ecc ecc

    I've already taken in consideration a carb rebuild because the previous owner never done it, but this point come later

    Thank you all

    David


  2. #2
    Myself's Avatar
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    120#'s on the GP1200 would be perfect for a stock engine. 100 is still OK and 115 would be normal for a used engine with those hours. It will probably have at least one creased check valve in the carbs and if it were mine I would delete the oil injection and go pre-mix. We have a mild ported '99 GP1200 that my wife rides and she really likes it.

  3. #3
    ok thank you

  4. #4
    Yamaha artisan Cutlass's Avatar
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    100psi might be ok, but that would scare me away. I would be ok with 115 to 120psi.

  5. #5
    Flying Scotsman's Avatar
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    It could have a head on it that would raise comp.if it did have 150-160 comp or even more then you would have to run high octane fuel.My 99 runs on 100+ octane.I would expect somewhere near 120 psi though and that will run on 87 octane.Most people remove the oil pump and mix there gas just in case they lose a oil feed line or the pump fails.
    What year is it ? and how about some pics.

  6. #6
    Hi guys....the situation is not so good...

    model is 1998

    I'm arrived at destination, the boy knows that we have to go at the sea to try the watercraft...

    But I got the gauge to test the compression, so I take off the seats and start to measure

    1) unplugged the caps, the sparks are not tighten..I can unscrew them with the hand.
    2) Removed the cyl#1 spark, smoke pop up from the cyl (bike was started few minutes ago I think..)
    3) the cyl#1 spark plug lateral electrode was totally missing!!! ...for sure the electrode was fallen in the cylinder and only God knows what's happens next...
    4) ...then I had misured the psi... #1 104 psi - #2 116 psi - #3 98 psi

    so...obviolusly I took time...and I said to him that if I take this craft, the price will be totally revised...now he want 2.000 euros with trailer

    Now the question is....if the bike has only 124 hours...

    in the worst case:

    2 pistons
    2 rings set
    2 cylinders

    better case...2 sets of rings (or 3...)

    what's the price?

    at which price do you consider this bike a good deal?

    thank you!

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  7. #7
    Myself's Avatar
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    My guess is that the carb adjustments were not opened up to compensate for the aftermarket flame arrestors. Those numbers and the fact that it still starts and runs lead me to believe there is no serious damage. Cylinders will probably be ok with a good hone. Worst case scenario new pistons and a few gaskets. Either way the motor has to come out and be partially torn down. That cylinder is a triple, you can't just replace 1, it's all 1 piece. And the seat needs recovered. I don't know what the going rate is for a waverunner over there but I'm thinking he's sitting on about 1,000 euro maximum worth of machine there. Which will be around 2,000 by the time it's fixed properly.

  8. #8

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    I would spend about $750-1000 depending on the rest of the ski.

  9. #9
    Yamaha artisan Cutlass's Avatar
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    That guy selling the ski seems like he is hiding something. Missing electrode, low compression, guy starts the engine shortly before you get there, and loose spark plugs. Its just difficult to estimate what is wrong. If you can test ride it and it rides ok, then its definitely a good one to buy to fix up. Then its probably worth 1200 euro tops. If it needs a crank and complete rebuild, then its worth about 400 euro...if my dollar-euro conversion is correct

  10. #10
    Flying Scotsman's Avatar
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    You did test comp with the throttle full open didnt you.If he neglected something as simple as spark plugs who knows what els is lurking in there for YOU to find.Either way it could cost you quite a few Euros so dont offer him a lot.2 ways to go buy something in great shape for big money or something with issues thats cheap that you know you can fix.

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