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  1. #1

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    Jun 2013
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    1999 1200 suv blew up Exhaust

    Hey I have been having problems with a 1999 Yamaha SUV. I had an oil line come off two years ago, and I rebuilt the motor and only went .5 over. I also rebuilt the carbs and everything was all but perfect when I sucked a tow line up in the drive and cracked a piece of plastic. Well go figure you can buy it so I had to make a new one. So I get that all done last year and put the ski in the river and it runs but seems to not want to run totally correct. So I winterize it and this year I put a new battery in it and check the compression and it is all good to go. I go to start it and have it fired up within 30 secs. Let it run a little maybe another 30 secs. and it full throttle and the motor dies. Then I start it right back up fires up no problem, ease into the throttle and hear a boom and I shut it down knowing that it was the water box with the exhaust. Well coming out of the metal exhaust water box there is two other plastic boxes before exiting the back of the ski. Well the plastic two both cracked and or blew apart. What is causing this as I had one blow before. The only thing that I can think of is too much fuel and it igniting after the water box. I am just tired of buying to just have them destroyed. Click image for larger version. 

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    I guess I posted in the wrong area at first. Let me know what you think could cause this problem.


  2. #2
    Yamaha artisan Cutlass's Avatar
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    Its backfiring out the exhaust. Thats why it blew up.
    Its caused by fuel igniting in exhaust. When you went WOT when running on the trailer and it died, it kept sucking fuel out of the carbs as the engine was winding down. That fuel went right into the exhaust and ignited the next time you started it.
    That kind of stuff is more likely to happen on land on a trailer then in the water. Avoid WOT on the trailer and it probably won't happen.

  3. #3

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    That is what I was figuring. I was also wondering what the two chambers do? (I am assuming that it is to keep water from running into the exhaust when you lay off throttle while underway) Is the a way to just run PVC from the rubber coming off the exhaust chamber to the rubber going out the tail. I would run it to the highest point and then back down. I am just trying to figure out if it is able to be done and not cause damage. The other option is when I get new ones to maybe put two layers of fiberglass on the outer side before installing it and it would be stronger. I also need to have the carbs. tuned. Is there a easy way to do it. Most places what over $300 to tune because they want to rebuild the carbs. I don't need them rebuilt as I have already did. Any help will be helpful.

  4. #4
    Yamaha artisan Cutlass's Avatar
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    I would guess the 2 chambers are there just to tune the sound of the exhaust. I can't see an other practical purpose. My GP just has a rubber hose connecting the water box to the exhaust outlet. I bet you could make something.
    Tuning carbs. Well if its a bone stock ski in good mechanical condition, the stock setup should work fine. No tuning required. If you have some mods or anything that engine related that isn't OEM, then post it here and maybe I can point you in a carb setup direction.

  5. #5

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    Well that's cool to know. I just bought the two new chambers from (crashhard). So they should be here today or tomorrow at the latest. I think I am still going to mess around with straight piping it. I believe that if I make the exhaust shorter from where it exits the water box to where it exits the ski it should be better. We will see. Anyways I should be on the water this weekend. It's about time. Thanks for all your help the next time I start it up will be on the water. I will let you know how it goes.

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