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  1. #1
    yamxlt1200nj's Avatar
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    Yamaha XL Limited Blown engine

    All, I have a 1999 yamaha xlt 1200 and I recently blew the # 2 cylinder this weekend. I'm looking at replacing the engine with a rebuilt SBT but wanted to get some recommendations on whether or not I should have the carbs rebuilt as well (as this could have been the root cause for the failure).

    I had the ski out last weekend for about three hours and it was running great. I noticed at the end of the ride the trolling speed had dropped below 1k rpms. This weekend I adjusted the idle to about 1100 rpms. I had it out for about 2 hours and noticed the idle bumped up to about 1500 rpms.

    Ran it for another hour at about half throttle and then opened it up for about 1 minute when the ski suddenly shutdown. It started back up but was bogging and would not get above 20 mph.

    Pulled the plugs when I got home and found the # 2 plugs looked like the piston had struck it. I pulled the head this morning and found the piston was severely damaged as it looked like the piston actually struck the head.

    So I was debating replacing the entire engine with an SBT and was wondering if I should also have the carbs rebuilt. I want to understand the root cause to avoid the same thing happening to a new engine.

    Any suggestion or recommendations are appreciated.

    --Brian


  2. #2
    Moderator OsideBill's Avatar
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    Welcome to the forum Brian.

    First off if you have some mechanic skills which it sounds like you do, repairing your OEM motor is far better then buying an SBT motor. Best case is a cylinder and piston, worst case is a crank and the above mentioned parts.

    Post some pics of the damage if you can, possibly this could be power valve related, but your description sounds like a midrange lean so it may be carb related.

    Lots of knowledgeable people here who will jump in and help.

  3. #3
    Hydrotoys's Avatar
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    +1.

    Don't do the "easy" route. You will regret it. Follow Bill's advice.

    It could be something as simple as you dropped a powervalve and just need one cylinder/piston, to something more complex as a crank. NOTHING is hard on a 2stroke, other than getting the damn pipe out of the boat.

    ...and welcome to the GH forums.

  4. #4
    yamxlt1200nj's Avatar
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    Yamaha XL Limited Blown Engine

    I attached some pics of the top end so you guys can take a look at the damage.

    I removed and cleaned the pv's this winter and I also have wave eater clips installed...I checked the clearance on the valves and it doesn't appear pv extended into the cylinder. I noticed the pv is damaged which appeared to be caused by loose debris from the damaged piston. I also noticed the # 3 piston has some damage around the edges and the sleaves are partially damaged as well.

    I was thinking a rebuild so I don't have to keep ripping apart the engine but if you think it's not worth it I'm open for suggestions. What are your thoughts on rebuilding the carbs. I'd rather have Bill do it since I don't want to worry about messing up the adjustment and causing further damage to any replaced parts.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by yamxlt1200nj; 05-24-2009 at 11:05 AM. Reason: Add another spark pic

  5. #5
    Hydrotoys's Avatar
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    Looks like a failed crank bearing to me. Go ahead and remove the center cylinder, (you can do this with the engine/exhaust in the boat,) and see if the crank has debris in the bottom.

    Probably nothing wrong with your carbs.

  6. #6
    yamxlt1200nj's Avatar
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    another pic of the sparks

    Can you tell from this pic of the plugs if it was running lean?
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  7. #7
    Hydrotoys's Avatar
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    not with crank bearings or piston rings bouncing all over the cylinder.

  8. #8
    L Carlson's Avatar
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    #2 looks like you spun the rings! OEM pistons tend to have this problem! When you pull the piston look for the little pin that would hold the rings. I bet it is resessed in the piston! I had this same problem last weekendLee

  9. #9
    yamxlt1200nj's Avatar
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    Thanks to everyone for these suggestions. I'm going to attempt to remove the # 2 cylinder to check the piston ring and crank. I assume I have to remove the exhaust manifold to pull out the cylinder?

  10. #10
    L Carlson's Avatar
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    Yes, The exhaust manifold will have to be removed. The two top 14mm nuts have stunds that are in the cyl. Time to have some fun turning the wrench!

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