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  1. #1

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    Yet another Hole in Piston thread (Piston #2)

    Hello! After a couple of months of searching for a good, active forum, I accidentally came across this one yesterday while googling "hole in piston". I have found my new home!

    Here's my problem:

    I recently acquired a 1994 Polaris 750 SL. I let it sit for about 8 months before I did anything with it. Finally a few weeks ago I got around to working on it - cleaned out the carbs, put a new battery in, new fuel filter, new spark plugs and just did an overall cleaning.

    I took it on the water and it ran pretty well. WOT for probably 25 minutes, ran fine. However, it was dificult to start. I noticed that with a fully, FULLY charged battery it started easily, but otherwise had a very hard time.

    Yesterday I took it on the water again and it ran like crud - very little power. It stalled out on me, but started right up again. I started heading back to shore when I decided to shut it off and restart it - but now it wouldn't restart. On top of that, the trim motor seal started leaking, so here I am in the water sinking quickly.

    Luckily, a boat comes by and tows me to shore. I get it home and try to start it up - it's TRYING but doesn't start.

    So, I pull out the spark plugs and in cyclinder 2, I find this:





    That's pretty bad - and then I look inside the plug hole and see this:





    So, here's what I think went wrong:

    1.) Wrong spark plugs.
    2.) maybe a lean mixture going into #2.

    I've searched the forums and everyone has had a problem with either Piston #1, or #3 - my problem is in #2. This Jetski has a single output fuel pump and no mods.

    What I'm hoping for out of this post:

    1.) Could this possibly be due to wrong spark plug or do I need to dig deeper?
    2.) I couldn't find any instructions on how to replace the piston. I am a total noob at this so a guide with pictures would be really helpful.


    Thanks in advance for any help!


  2. #2
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Welcome to the Green Hulk. You found the right place
    Looks like it was burning super lean. What was the part # of the plugs? Can we see pics of the other plugs?
    You will want to change all the fuel lines, and clean the fuel pickup in the tank. Replace the pump w/ a 3 outlet pump. Replace pulse line to the pump, keep it no more than 10"s long. Clean the filters in the carbs.
    Also will need to rebuild or replace the fuel shut off valve.
    Pull the head and lets have a better look at the damage.

  3. #3
    2&4strokepolaristech's Avatar
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    1994 Sl 750

    the first thing you need to do is to pull that fuel pick-up(where the fuel lines go into the tank) out of the tank and make sure the lines are still on the end and that they are in good shape. I would replace them either way if you have not done so in the past 3 years. let us know what you find and take some pictures. We all love pictures.

  4. #4
    Moderator beerdart's Avatar
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    Welcome to the hulk.
    The wrong plug should not cause a hole in the piston you need to dig deeper.
    The manual can be downloaded from the tech section. You should upgrade the fuel system to the three outlet design. Post a WTB in the classifieds for the parts you need after you pull the cylinder and see if it is reusable.

  5. #5
    2&4strokepolaristech's Avatar
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    starflight beat me to it! Damn you guys are so quick!!!! you will not find a better bunch of guys on ANY forum ANYWHERE than this Polaris PWC forum!!!!

  6. #6
    100 MILES OF HEAVEN AND I AM SMACK IN THE MIDDLE KEYZBUM's Avatar
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    WELCOME TO THE HULK
    I would say you ran lean on that cly.
    with #3 and #1 it can be a seal letting air in or evan an index problem,,,
    but with just #2 burnt again I would say replace piston and either do your carbs or send them to randy so they get done right!!!
    others with more info will be by shortly with more "correct" help
    I am the local hack here oh and head south 1 1/2 hours and we can take a ride
    have fun and welcome
    mattman
    i type slow they all beat me anyway lol

  7. #7
    2&4strokepolaristech's Avatar
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    I Am Talking Minutes Apart!!!!! =d>

  8. #8
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Looks like an autolite plug. You will need (most recomended) NGK BPR8ES plugs.

  9. #9
    Moderator beerdart's Avatar
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  10. #10
    Moderator beerdart's Avatar
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    Don't scare the new guy!!!!

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