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  1. #1
    Nickeljet's Avatar
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    Help!! 780 burns hole in #1 piston

    I am working on a 780 Polaris. It had a hole in #1 piston. I changed the piston & it ran for a little while but had to run it on choke after about 10 minutes. I brought it in and #1 had another hole in it. I have replaced the piston again but it still only runs on choke. Osidebill says you guys are the best. Thanks for any input.


  2. #2
    100 MILES OF HEAVEN AND I AM SMACK IN THE MIDDLE KEYZBUM's Avatar
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    the carbs need to be checked...and cleaned
    and a triple outlet feul pump needs to be added so ypu dont hole another piston
    running with the choke on is a shure bet the carbs are dirty
    look into clean carbs,new fuel lines,triple fuel pump
    mattman

  3. #3

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    What year and model 780 ,i think all the 780's came with a triple pump . Clean the carbs and replace the fuel lines and take the fuel selector switch out and make sure it's not clogged up

  4. #4
    Moderator beerdart's Avatar
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    The 780 had a triple fuel pump stock.

  5. #5
    Nickeljet's Avatar
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    Thanks guys

    The ski does have a tripple fuel pump & it is producing well. The carbs may need cleaning. I will try this next

  6. #6
    Moderator OsideBill's Avatar
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    Thumbs up

    Quote Originally Posted by Nickeljet View Post
    Osidebill says you guys are the best. Thanks for any input.
    Steve these guys will take great care of you. Best Polaris minds on the planet here.

  7. #7
    Nickeljet's Avatar
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    No worries

    You have never steered me wrong yet Bill. I think we need to vote you forum member of the year!

  8. #8

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    Quote Originally Posted by Nickeljet View Post
    The ski does have a tripple fuel pump & it is producing well. The carbs may need cleaning. I will try this next

    Make sure you check that fuel valve

  9. #9
    Nickeljet's Avatar
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    I removed the intake hose from the fuel pump and put it directly into a gallon of fuel. No difference so I kinda eliminated fuel tank trash or fuel valve problems but I really apppreciate your input

  10. #10
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Which cyl are you calling #1? MAG or PTO?

    Check the carb settings to the on line manual in the tech section. Maybe someone "adjusted" it/them and fouled up.

    Like the guys mentioned, I would be inspecting the fuel hoses and filters for obstruction.

    Next in line would be the fuel selector valve. Check to be sure it's not clogged.

    Then look for loose hose connections. A loose connection can suck air causing a lean condition.

    Thoroughly clean the carbs, front and back. Inspect the diaphragm for cracks or brittleness. Inspect the fuel filter inside the carbs.

    Make sure the needles are in good condition, and not stuck.

    Perform a leak down test to look for any air leaks. This is a common issue for old rear crank seals to leak. Also pay attention to intake, head, and base gaskets.

    If all checks out good, then you need to do a crank index. Checking to see if the crank is out of phase from possible hydrolock or a stick jambed in the jet pump.

    Let us know what you find.

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