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  1. #1

    Join Date
    Jul 2006
    Location
    West Bend, WI
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    40

    Melted pistons - need carb setting advice

    Hello again. Posted here this summer about a hesitation problem with my '99 GP1200 and got a ton of help. Turns out it was the shop that rebuilt my ski didn't check popoff pressure and had the wrong springs in (115gr vs. 95gram). I replaced them myself, but in doing so decided to pull the head to check and see how things were going. Bear in mind that since getting the ski back, it never ran right and I only had put about 5 hours on it since the shop did the rebuild. When I pulled the head I found the first two pistons were melted again. I was PISSED. So I contested the charge on my credit card with the shop because they said it was my fault and took it to another shop. I'm in the process now of getting it fixed and want to NOT have this problem again. SO - I'm looking for some help on values for jets and needles for the carbs.

    Upgrades I've done -
    K&N Flame arrestors
    Pre-mix
    Solas XO prop
    ADA aluminum head 42cc domes

    Current carb settings that caused ANOTHER meltdown:

    115 gram springs (I changed to 95 gram springs which fixed the bogging)
    1.5 needle and seat
    100 pilot jet and
    135 main jet.

    To avoid this expensive issue again - what should I use for needle/seat and jet settings??

    Thanks!


  2. #2
    Flying Scotsman's Avatar
    Join Date
    May 2006
    Location
    IllINOIS
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    Melted pistons is usually lack of fuell.
    It sounds like you had an air leak did you pressure test the motor..
    Are they stock carbs.

    Im looking for jetting specs for 46mm mikunis with F/A no chokes and 150 psi.

    SCOTT..........
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  3. #3

    Join Date
    Apr 2006
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    panama city beach 'fl
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    Cool

    make sure to check fuel pump ,Any distorting of diaphragms will give poor/no fuel pressure


    later cd

  4. #4

    Join Date
    Dec 2005
    Location
    Beaufort, SC
    Posts
    119
    Your jetting looks right for your mods; what are/were your mixture screws set at?

    I'm with Scott & Chip, you might have a different problem elsewhere. Can you describe how the piston was melted? Just a little off the top in front of the exhaust port?

  5. #5

    Join Date
    Jul 2006
    Location
    West Bend, WI
    Posts
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    I've got pictures - how can I post them?

  6. #6
    ....back from the dead.... J-ME's Avatar
    Join Date
    Aug 2005
    Location
    Delaware
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    The manage attachments bar under additonal options.

  7. #7
    here is same advice gp1200 melt piston is most due to
    a crest on the fuel pump
    the stinger on the pipe dont let in of water true (san and salt deposits )
    or on the rebuild they use a aftermarket exuste gasket and is from a 1100 not a 1200

  8. #8
    spud's Avatar
    Join Date
    Jul 2006
    Location
    Oceanside, California
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    It does sound like something else is wrong. Your jetting doesn't look bad. I had a 100, 102.5 and 105 for pilots, 1.5 N&S 95 springs and 135 mains.

    High screws were 1, 3/4, 1 1/8

    Low screws were all from 1 to 1 1/4

    My seizures happened at 1/2 throttle, never at full throttle. After going up on the pilots the problems went away.

    I think you have another gremlin- air leak etc.

  9. #9

    Join Date
    Dec 2005
    Location
    Beaufort, SC
    Posts
    119
    Bill, I thought that the 1100 gasket was preferred because it had larger water passages on the rear cylinder (or is it the middle one)? I've used an 1100 gasket on my 1200 before.

  10. #10

    Join Date
    Jul 2006
    Location
    West Bend, WI
    Posts
    40
    I did notice on the ADA head that the 3rd cylinder had some fuel/oil(?) mix coming out the top of the head through the bottom of the spark plug where it screws in. It was due to the rubber o-ring gasket not being seated properly by the shop. This is why I pulled the head in the first place, to reseat this - that's when I found the burned pistons. Is that enough of an air leak?

    According to the new shop the first two pistons are burned on the exhaust port side.

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