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  1. #1

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    06 STX 12F Popping and surging

    New to the forum, and have already received a ton of great information, so thank you.

    I have an 06 STX12F that a friend gave to me (not sure if I should thank him yet). A little history on this ski. He purchased an SBT stock crate motor for the ski, and got it professionally installed. Took it out, and it ran for a while (.5 hours or so). Got back on it, and it wouldn't turn over. Smoke started coming from the starter terminal. I think this was the last straw for him, and he asked me if I wanted it.

    I pulled the motor. Spun it on the cherry picker by hand, and it felt fine. I tried to spin the impeller shaft, and it was frozen. So I pulled the jet pump, and completely rebuilt it. Spins beautifully now. I purchased a new starter, since the insulation was melted on the (+) post on the old one.

    I put everything back together, and it would not start. I pulled a plug, and played it on the head to check for spark. Everything was fine. I pulled the fuel line, and nothing was coming out. So I ordered a fuel pump. When I installed that, it fired right up. Here is were the problem begins.

    When I start it, it starts to pop, and immediately wants to rev to like 5K. I pulled the intake to make sure there was nothing missing or loose. I checked the throttle body for leaks. I pulled the ISC and blocked the crossover just to rule that out. Nothing made any difference. I read on another thread about a guy that disconnected his O2 sensor (actually a water temp sensor), and it reduced the revs, but kicked an FI error (obviously). Then I pulled the actual sensor, and it was covered in oil. I cleaned the oil off of it, and re-installed it. When I plugged it in, it immediately popped and raced again. When I pulled the sensor again, it had oil on it again.

    I have seen a lot of threads come close, but addressed my issues.

    1) Should I be concerned about oil on my water temp sensor?
    2) What could be culprits to the surge and pop? (I can't see anywhere else where it could be leaning out). Obviously it is something I did or did not do, or it wouldn't have ran for the .5 hour on his last outing.

    If anyone wants to see it run, shoot me your # and I will be glad to text you a short video.

    I just want to add that while the engine was out, i performed a leak down test on all four cylinders with good results. I have also verified that all spark plugs are properly torqued.
    Last edited by bborner; 02-07-2019 at 08:09 PM.


  2. #2
    Take the time to smile sirbreaksalot's Avatar
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    all the temp sensors on the engine HAVE oil / grease to transfere the heat to the sensor, with out the lube they WILL NOT read correctly !!!!!

    remove the airbox and ensure the Throttle plate is actually all the way closed as it supposed to be.

    check to see if the 10mm bolt is in the inlet manifold (used to drain water if you flood the ski )
    hasn't fallen out...….. doubt that would get u too 5k rpm

    there is also a bypass screw on the bottom of the Throttle body that some youtube mechanics stuff with , with out the required knowledge on how to set correct idle on these skies ( check that ) you con block the holes in the throttle body with filter removed... they are on the lower area of the TB

    air is somehow getting into the engine ( more than normal idle amounts )...… just use basic mechanical diagnosis and follow the air...

    post the video on here...……….

    Waz

  3. #3

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    I will take a short video, and post it later today. But to answer some questions:

    1) Good to know about the oil on the sensors. Curious though, if I wiped it clean, and it was re-coated with oil after the second run. Doesn't that mean their is oil flowing through the passages? I am pretty sure that should not be in a water passage. I can understand if it was pre-coated upon install, but I wiped that off.

    2) I have been running without the airbox on while diagnosing. The throttle plate is coming to full close. I even blocked off the ISC crossover channel in the plate with a rubber plug to make sure that wasn't the culprit. If anything that would starve it of air, but it still surges immediately. I have never touched the adjustment screw on the bottom of the throttle body, so I doubt that is the issue.

    3) The water drain plug is tight, as well as the plate screws on the bottom of the intake box.

    The only new addition is the replacement fuel pump. I don't have the adapter to test the fuel pressure, but I know it is getting plenty (fuel line immediately goes taut). I even pulled the fuel injector rail, and pulsed it with the starter to make sure that it gave a consistent puff of gas out of each one on to a clean blue paper towel.

    I just can't imagine where that much air could be getting in without something very obvious. But I will do some more work later today, and provide the video as stated.

  4. #4

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    Here is the link to the video. On the last surge, it would have kept climbing if I had not hit the kill button. By the way, I never touched the throttle throughout the video.

    One more interesting tidbit. If I place my hand over the throttle body opening, I can feel the vacuum (obviously), but it will still run, and surge.

  5. #5

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    I have to close the loop on this at my own shame. The key giveaway was putting my hand over the throttle body, and having it still run. I pulled the throttle body, went over it thoroughly. Everything looked good. So I pulled the intake, verified everything was tight and plugged as it was supposed to be. I pulled the gasket and verified that it still looked good. When I was convinced everything looked good, i went to put it back together. That was when I noticed the four washers for the nuts sitting flat against the block. I did that so I wouldn't lose them when I pulled the motor. As you can see from the angle of the video, I was working from the left side of the ski (due to space), so I did not look at the surface of the block when i disassembled several times.

    Low and behold, I took the washers off, placed them back on the outside of the intake manifold where they belong, and the thing runs like a dream.

    Another sacrifice of several hours to the diagnostic gods, and lesson learned as a shade tree mechanic.

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  7. #6
    steve45's Avatar
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    Don't feel bad, we've all done dumb stuff. Actually, that didn't sound like a dumb idea at all--kept you from losing the washers.

    Thanks for reporting back, may people never tell us the final outcome of a problem.

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  9. #7
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    this demonstrates why you want to turn off your cell phone and close the doors when you are assembling something. the slightest distraction and you end up screwing several hours of your life up

    I also have significant experience in this area

  10. #8
    RLACEMAN's Avatar
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    Or one of your friends stops by to tell you his latest chapter of dismal life, just shut the tool box at that point & drink beer with him.

  11. #9
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    Quote Originally Posted by RLACEMAN View Post
    Or one of your friends stops by to tell you his latest chapter of dismal life, just shut the tool box at that point & drink beer with him.



    that's assuming he's got a 12 pack in tow

    before I show up at my buddies place, I call his wife and ask him what's he's up to.

    if he's knee deep in an out drive ( he's a big boat tech) I hold off until it beer:30

    for a while it seemed ever time I was trying to get some carbs on a 787 my mom would call

  12. #10
    Bucky STX-15F's Avatar
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    Glad you figured it out, it always seems to be something simple. Right?
    i remember years ago replacing a car battery...sounds easy enough, but when i went to start the car with the new battery nothing happened! what!
    a week later and several parts bought i found one "extra" wire that was supposed to connect to the positive side was laying along side of the battery...hooked it up and the car ran fine. new parts and all.
    thanks for the update.

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