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  1. #1

    My 720 GTI Autopsy

    I just finished rebuilding my 720 in our 97GTI complete with new cases, crank, fresh top end etc. Dropped the motor in over the weekend and went for a fresh water lake test on Sunday.

    The ski died after 15-20 minutes of riding (mid throttle max). Wouldn't restart at all - a couple times it almost fired but didn't.

    Compression test last night showed about 118psi on both cylinders, found water laying in the spark arrestor holder, pulled the heads and realized I forgot the two o-rings around the pistons!

    Obviously it got water in the cylinders - question is how bad did I hose this engine up? What steps should I take right now?

    Thanks!!


  2. #2
    wkuadam07's Avatar
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    Pull it apart and see what else you forgot... LOL

  3. #3
    Thanks! I deserve that! I've torn into this motor so many times chasing one problem after another and have so many old gaskets laying around, I just didn't pay too much attention when putting the head on. Long day and night putting her back together didn't help either.

    It ran sweet for 20 minutes! I took the top end and carb off and used a heat gun to heat the crank and cases up real good last night to lose any moisture - everything looks and feels good - so I'm pretty hopeful that it'll be alright!

  4. #4
    wkuadam07's Avatar
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    Are you trying to do this inside the ski? Cause that's mistake #1... just my opinion. I always take them out and take my time... saves me $$$.

    If the pistons look ok and the cylinders aren't trashed it's probably going to be just fine when put back together.

  5. #5
    yeah, the motor is still in the ski - I pulled the jugs off and the crank case is dry as a bone. The cylinders look great, pistons look great so I will re-assemble to check comp levels and go from there. The only thing in my favor is that I just rebuilt and had a lot of assembly oil (amsoil) on everything and was pre-mixing very heavy.

  6. #6
    dolson's Avatar
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    Did you run it off a hose At all

  7. #7
    no, never ran it off a hose - I don't have it set up for a hose.

  8. #8
    Update. Put it all together got it to start, runs real rough, and pretty sure the rear cylinder was not always firing. The ski will not rev though and dies with any throttle above idle. Plugs look super black and wet after running a couple seconds in the driveway. I get gas blowing out the top of the carb too at times. I did a quick carb clean and no change. Also, when I pulled it apart after the water ingestion there was a puddle of water in the tray that the air screen sits in. Need help! Thanks!

  9. #9
    wkuadam07's Avatar
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    Did you leak test and pop off test the carbs?

  10. #10
    Update: wasted the brass rotary gear - not enough oil in the tank. Rotary valve was never moving! I hope this is as much fun to ride as it is to work on!! Putting it all back together now - cant wait...

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