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  1. #1

    Gp1200r subtle knock with engine vibration

    Hello hulk nation.

    Just got done doing a complete top end rebuild and fired it up for the first time today. Started up fine, compression is perfect at 115 in all 3 cylinders. It idles beautifully except for a slight knock with vibration every once in a while. The knock doesn't have a particular rhythm to it and it doesn't always do it. The vibration isnt crazy bad it's just slight and it's always in time with the knock.

    The fuel that's in it has been sitting over the winter with stabil in it.

    Any ideas on the sound/vibration would be super helpful. I can't remember if it has always done it or not.


  2. #2
    Any ideas?

    I was running water through it to see if there were any water leaks anywhere without the engine running. Big no no?

  3. #3
    lukejaeger1's Avatar
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    If you ran water through it with the engine off you probably filled the engine with water. Did you start it after you had the water on? I did this once before I knew any better and ruined the engine.

  4. #4
    I did run it about 5-10 minutes after running water through it.

    I didn't know any better either. Found out after doing a little research on this knock.

    Gonna pull it apart tomorrow and check everything.

  5. #5
    lukejaeger1's Avatar
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    Hopefully you didn't cause too much damage. I put mine in the water and rode for awhile before it locked up. It cracked the case and burned up 2 cylinders and pistons. If only I'd known better....... The sooner you can get the water out of there the better. Best of luck.

  6. #6
    Also, cylinder 3 (I think, the one towards the rear of the ski) was running a bit hot compared to the other 2. So I took off the heads and inspected the cylinder. The 2 "corners" closest to the exhaust port were slightly worn. These are brand new pistons, rings, and honed cylinders. I suspect it to be early signs of seizure in that cylinder only.

    I've researched many times on here and google and haven't found a definitive reason for this. Detonation, pre-ignition, lack of cooling, a lean condition all seam to be the normal cause. I've taken Out the carbs and will rebuild them and clean them.

    Anyone have any input on why this could be happening?

  7. #7
    lukejaeger1's Avatar
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    When you say "corners" by the exhaust port do you mean the powervalve? Your powervalve may have fallen and might be rubing on the piston. Believe it or not this also happened to me. The powervalve broke off of the shaft and ruined the piston among other things.

  8. #8
    No the power valves are intact. The markings are on both sides of the exhaust port on the cylinder wall.

  9. #9
    slothman's Avatar
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    knocking could be from detonation. DO NOT run that ski any more until you solve the problem, or you will just make the problem worse.

    Have you rebuilt the carbs yet? This is a must to make sure the ski runs good. If one of the carbs is plugged up, it could run lean and cause the knock you are hearing.

  10. #10
    I haven't run the ski at all since hearing the knock/vibration. Took the heads off and noticed the marring on cylinder 3 which was running hotter than 2 and 1 when it was idling. Took the carbs off and apart and noticed some small balls of gelled fuel in them. Waiting on the rebuild kits and ez tune adjusters.

    When I checked the adjusters the lows were out about 1 1/2 and the highs about 1 3/4. High jets are 125 and lows 110. 1.5 n/s with I believe 95 gram spring.

    Any ideas on the cause of detonation?

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