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Thread: RPM gone crazy

  1. #1
    Petron's Avatar
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    RPM gone crazy

    I think I have a serious issue here and really need your help.

    My ski has been running great since the start of the season.

    Today, I was flushing it and upon giving it some throttle at approx. 6500 RPM then letting off the throttle she just peaked to maximum RPM and wouldn't stop.

    I shut off the water, pulled the laynard off and it would'nt stop. The only way she'll stop is to hold down on the throttle and it'll go into a stall mode. Nothing wrong with the throttle cable, at all.

    Possibly a serious issue because if it happen's out on the water who knows? I ohmed out my start/ stop switch and it rang out fine.

    I have all new fuel lines, carbs recently rebuilt, new gaskets, filters etc.

    I really need your input on this matter, greatly appreciate it.


  2. #2
    Chaserxp215's Avatar
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    happend to me. As long as it is water itll be fine. You either have an air leak...someone will chime in. I forgot where but mine was the throtle cable just being a little bit too tight.

  3. #3
    I am having the same issue on a 97 GTX. Took it to a mech and he stated it was a timing issue but could not adjust it because one of the pistons was damaged. Just reinstalled a warranty claimed SBT motor set the timing per instructions and still have the same issue. I am taking it to the mechnic to have him review on Tuesday. Will let you know the results but I have to assume it has something to do with the carbs.

  4. #4
    Petron's Avatar
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    Any specific area around the carb I should be looking at? I had a look around and didn't see any noticable air leak.

    So why when you take the laynard off it doesn't shut off?

    Why doesn't it happen while in the water?

  5. #5
    mibunkerking's Avatar
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    if your throttle cable is good then your runnig way lean. either because the filters in the carbs are clogged, mixture is off, or you have a air leak.

    the reason that it doest stop and keeps running away i because the tip of the spark plug has gotten so hot that it ignites the gas without sparking. called glow pluging. one way to stop it is to add more fuel. ie open the throttle. scared the carp out of you when it kept going didn't it?

    was it making a metal pig sound when it was running away? if so it was probably DETOing which could mean you have a air leak. did you check the fuel mixture after you rebuilt the carbs by doing a plug chop? i would start there. chances are that the low and high sped screwes were not reset correctly after the rebuild.

    do not run it on the water till you fix the problem. a lean mixture in a 2 stroke means no lubrication. it wont show up on the water because the motor is under load. its hard to notice if its running lean until you seize a piston at WOT. not good day.

    wolfiedog...you should fire your mechanic.

  6. #6
    Petron's Avatar
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    mibunkerking...the reason that it doest stop and keeps running away i because the tip of the spark plug has gotten so hot that it ignites the gas without sparking. called glow pluging. one way to stop it is to add more fuel. ie open the throttle. scared the carp out of you when it kept going didn't it?
    Yes....it made me shit my pants, thought it was going to blow up.

    mibunkerking...was it making a metal pig sound when it was running away?
    There was some sound going on yes, I was so caught up trying to shut it off it blurred my concentration a little.

    mibunkerking...did you check the fuel mixture after you rebuilt the carbs by doing a plug chop?
    Please define plug chop..& best method of checking fuel mixture? (has oil pump, setup on the mark)

    mibunkerking...chances are that the low and high sped screwes were not reset correctly after the rebuild.
    Set up as per manual. High speed set up in fully seated position & low speed about 3/4 to 1 turn away from fully seated.

    -Appreciate your input & others too.

  7. #7
    mibunkerking's Avatar
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    turn your low speed screws out till it idles smooth and comes down from throttle on the trailor. turn both in all the way and back out 1 turn to reset them to a good starting point. go out a 1/4 turn till it settles down. dont go more than 2 turns out though. mine are set at 1 1/4 out on both. once you get it idleing and responding nice, take it to the water for a plug chop.

    a plug chop is a test useing the plugs color to check the mixture. put it in the water and warm it up with new plugs. do a WOT run of about 5 secs first. pull lanyard while holding the throttle wide open till you come to a stop. pull the plugs and look at the porcelain insulator. you want choclate brown. white your lean, black your rich. if it white, you are risking a seizer and DETO.

    now adjust your high speed screws according to the color. once you get it close to brown, increase the time of the WOT to 10,15,20 secs and so on to confirm and fine tune. this should get you dialed in on the mixture.

    while you are on the water doing the tests, esp. at WOT, listen for a metal ping sound. you may have to turn your head side ways to hear it. if you do hear a metal ping sound then its DETOing.

  8. #8
    Chaserxp215's Avatar
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    Quote Originally Posted by mibunkerking View Post
    a plug chop is a test useing the plugs color to check the mixture. put it in the water and warm it up with new plugs. do a WOT run of about 5 secs first. pull lanyard while holding the throttle wide open till you come to a stop. pull the plugs and look at the porcelain insulator. you want choclate brown. white your lean, black your rich. if it white, you are risking a seizer and DETO.
    Is that what nascar does like after there qualifying runs when they just kill the motor and coast back to pit road in neutral?

  9. #9
    Former 2 stroke hater!
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    Thats a lean runaway condition, the best way to stop it is to choke the engine, it flushes the cylinders with fuel flooding them cooling the plug and it will die fast. You either have a lean condition on the high speed settings or probably a seal leaking around the crank, because the engine may be getting air through somewhere other than the carbs.

  10. #10
    Petron's Avatar
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    Update - I had a day off today and decided to work on my ski.

    The closest thing I found to an air leak was the flame arrest housing allen screws were loose (unthreaded). I disassembled it, applied a coat of loctite 518 and put it back together - had to re-tap the threads and purchased slightly longer allen screws, threads were screwed up.

    I adjusted the low speed screws, did a plug chop and slightly opened my high speed screws accordingly. I adjusted my throttle cable as well.

    When I'm flushing she idles great now with no increase or decrese of RPM without my influence, gave it some gas and she'd go back to idle perfectly, hit 6500 RPM and no run-away experienced, right back to idle.

    Thanks for the help guys .

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