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  1. #1
    Chris03HD's Avatar
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    Waterbox & Sound Suspression ON - Now Backfires Bad!

    Just about water ready with this '99 XLL 1200.

    Started it up for the first time on Saturday, without anything after the stinger connected yet... seemed fine except for a hesitation.

    Finished installing the waterbox and SS so I could run it without the carbs sucking exhaust fumes and run it on the hose.

    Every couple seconds it will backfire (out the exhaust) bad and this is while idling.

    Seems to be quite a bit of air in the fuel lines, just rebuilt everything and new filters and hose.

    Also when I went to put gas in it today, the gas cap just about rocketed off when I opened it!

    Suggestions?


  2. #2
    Mpeavler's Avatar
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    1. Did you pressure test the engine 10psi for 10 minutes?
    2. Is it running so rich that it's filling the box up with fumes of fuel/fuel leading to the issue
    3. Does it idle normal...any wondering or surging up or down?
    4. Where is your bottom needles at?
    5. There should be no air in the lines...."fuel" after only a few seconds of running.
    6. Check valves may be shot if it's popping up through the carbs is it?

  3. #3
    Chris03HD's Avatar
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    Quote Originally Posted by Mpeavler View Post
    1. Did you pressure test the engine 10psi for 10 minutes?
    2. Is it running so rich that it's filling the box up with fumes of fuel/fuel leading to the issue
    3. Does it idle normal...any wondering or surging up or down?
    4. Where is your bottom needles at?
    5. There should be no air in the lines...."fuel" after only a few seconds of running.
    6. Check valves may be shot if it's popping up through the carbs is it?
    Ill answer the best I can. Keep in mind I was originally told this ski, "only needed the carbs cleaned, and then reinstalled", when i bought it.
    As you can see from my other post, there were many issues that popped up along the way.

    1. No.
    2. No, only started backfiring once I put the waterbox and ss back on today.
    3. Yes, very smooth actually.
    4. One turn out.
    5. The lines filled very quickly when I fired it up for the first time after everything being apart, but I have noticed air bubbles in the line while running. Also, the 1/4 T for the additional fuel pick up, that filter and line is bone dry.
    6. Carbs were completely rebuilt. The two check valves inside the pump and the tiny one on the block, also replaced.

    The only other "difference" is I had the white check from vent off the pickup tube.

    Thanks M!

  4. #4
    Mpeavler's Avatar
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    1. I would pull the engine back and do this if it were me. An airleak can cause it to burn up quickly although usually you will get surges at idle...and once it get's hot..usually a "Run A Way" engine following quickly afterwards if hot and lean. I think just to know that it was sealed up and hassle free...I would pull it. The kits to test can be made for $30

    2. Well once you put the rest of the exhaust on, it helps create back pressure and I would not run a 2 stroker without the exhaust on moving forward "wink". This tells you something is going on with the fuel system somewhere if it only does this with the exhuast on.

    3. I'm surprised about this...although you could turn the low speed adjusters out to 2 turns to verify that it's not from being to lean. If it get's worse...then you could be just rich. Does it pop up through the F/A 's ?

    4. Try "2" turns out and see if it get's better.

    5. That may go away once you put a load on the engine and actually pull some fuel through the lines. I would not stress to much although, it's odd it filled up and now is drained though? You stated you have good positive pressure on the tank so have you checked the valve "one way" to make sure it's working?

    6. Bill did these carbs for you?


    Quote Originally Posted by Chris03HD View Post
    Ill answer the best I can. Keep in mind I was originally told this ski, "only needed the carbs cleaned, and then reinstalled", when i bought it.
    As you can see from my other post, there were many issues that popped up along the way.

    1. No.
    2. No, only started backfiring once I put the waterbox and ss back on today.
    3. Yes, very smooth actually.
    4. One turn out.
    5. The lines filled very quickly when I fired it up for the first time after everything being apart, but I have noticed air bubbles in the line while running. Also, the 1/4 T for the additional fuel pick up, that filter and line is bone dry.
    6. Carbs were completely rebuilt. The two check valves inside the pump and the tiny one on the block, also replaced.

    The only other "difference" is I had the white check from vent off the pickup tube.

    Thanks M!

  5. #5
    Chris03HD's Avatar
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    Quote Originally Posted by Mpeavler View Post
    1. I would pull the engine back and do this if it were me. An airleak can cause it to burn up quickly although usually you will get surges at idle...and once it get's hot..usually a "Run A Way" engine following quickly afterwards if hot and lean. I think just to know that it was sealed up and hassle free...I would pull it. The kits to test can be made for $30

    2. Well once you put the rest of the exhaust on, it helps create back pressure and I would not run a 2 stroker without the exhaust on moving forward "wink". This tells you something is going on with the fuel system somewhere if it only does this with the exhuast on.

    3. I'm surprised about this...although you could turn the low speed adjusters out to 2 turns to verify that it's not from being to lean. If it get's worse...then you could be just rich. Does it pop up through the F/A 's ?

    4. Try "2" turns out and see if it get's better.

    5. That may go away once you put a load on the engine and actually pull some fuel through the lines. I would not stress to much although, it's odd it filled up and now is drained though? You stated you have good positive pressure on the tank so have you checked the valve "one way" to make sure it's working?

    6. Bill did these carbs for you?
    3. No, backfires while idling, out the exhaust.
    5. Only the extra (1/4" T line) is bone dry.
    6. No, I did the rebuilding and jetting myself like I've always done.

    Added more info to the post, maybe while you were typing your responce..
    The only other "difference" is I had the white check from vent off the pickup tube.

    I pulled it after the gas cap almost rocketed across the garage, and forgot to plug in back in.

  6. #6
    Mpeavler's Avatar
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    1. I would pressure test it since the ski is not what you "thought" or was "told" you were buying. Better to be safe IMO then sorry this coming Summer.

    2. I would still question that air pocket in the carb....are you sure you got those check valves seated good in there and the arm on the needle was flush with the jet block?

    3. What's the plugs look like right now...any of them washed out?

    4. Are you sure your getting spark to all 3? Sometimes when no load it will sound fine...but your missing or having an intermitten spark...leading to excessive raw fuel in there...and then POW?

    5. Pop up through the carbs??

  7. #7
    Chris03HD's Avatar
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    Quote Originally Posted by Mpeavler View Post
    1. I would pressure test it since the ski is not what you "thought" or was "told" you were buying. Better to be safe IMO then sorry this coming Summer.
    2. I would still question that air pocket in the carb....are you sure you got those check valves seated good in there and the arm on the needle was flush with the jet block?
    3. What's the plugs look like right now...any of them washed out?
    4. Are you sure your getting spark to all 3? Sometimes when no load it will sound fine...but your missing or having an intermitten spark...leading to excessive raw fuel in there...and then POW?
    5. Pop up through the carbs??
    2. Yes sir. Im hoping once I get it on the garden hose tomorrow, I can run it for longer then a few seconds. Maybe then everything will be full and primed. Ill also plug the check for vent back in as well.

    3. Plugs are brand new looking.

    4. Tested spark before trying to run it the other day. All three were showing good spark, and I'm using a strong battery.

    5. No pop. Nothing coming from carbs. Also, reeds looked perfect before installing carbs.

  8. #8
    Mpeavler's Avatar
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    Makes me nervous...

  9. #9
    Moderator beerdart's Avatar
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    Have you checked the flywheel?? I hate buying skis the just need the carbs cleaned.. I would go over everything and pressure test. Compression test?

  10. #10
    cheatin' piston popper addicted's Avatar
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    does it have a cat or dplate? if it still has the cat, is it intact, or are parts of it lodged in the stinger?

    are you sure it's a backfire, and not normal popping?

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