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  1. #1

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    Yamaha GP1200R burning pistons with R&D head? Compression to high?

    Hi all what must the ompression be not to burn pistons it has burnt 2 pistons not even running 10 minutes. It has a R&D head installed and i am thinking compression is to high? is there anything else i must look at?


  2. #2
    Mongoose's Avatar
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    What are the hours on the ski?
    R&D heads should be giving you about 150psi-if their the cast ones-IF youve got the ones with interchangeable domes-check what cc domes youve got.
    Fuel octane may not be high enough.-You would need 93 octane US spec or 98 octane UK spec for the higher compression heads-don't know about ratings in SA.
    Carbs may need a rebuild.
    Air leak causing ot to run lean?

  3. #3

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    Hi there...the heads are 150psi the cast ones. We have here 95 octane running.
    Any idea what the pilot jetting must be on the carbs?
    I will have a look at the carbs when it is off now to rebuild.
    It ran 10 minutes with the new pistons i fitted 3 but it only burnt no1 badly.
    Thanks for the tips.......

  4. #4
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    95 octane is ok for 150psi....98 is safer though if you have advanced the timing as well.

    has to be something else.

  5. #5

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    Thanks for replying back to me does any one know what the pilot jets has to be?
    And will it be the wrong jets perhaps causing it to burn the piston up?

  6. #6

  7. #7
    Mongoose's Avatar
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    Yep-checked my old notes-you wont go wrong with 110 pilot, 120 main, 1.5n/s and 95 gram spring.
    Start with highs and lows out 1.5 turns. Also note these specs are with the POS accelerator pump dissabled. Also a good tip is to double up on the check valves(put one on top of the other) Do all this with a rebuild kit and you will know it's not a carb issue!

  8. #8

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    Thanks everyone for the helpfull info keep well and drive like you stole it.......................

  9. #9
    Wish I found this thread before putting second hand [email protected] heads on my freshly rebuilt gpr and running 91 octane fuel. 2 pistons fried in 5 minutes .

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