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  1. #1
    way2much2do's Avatar
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    Question 95 SLT750 - Sluggish Throttle Response after being inverted

    Ok all you carbureted 2-stroke geniuses, I've got a good one for you.......

    Was riding my 95 SLT 750 today. Ran fine all day. My nephew was on the back and asked for a more aggressive ride so I did. We ended up flipping the machine. I quickly pulled the lanyard, so it only ran for a few seconds upside down. I flipped it back over quickly (approx. 10 seconds after pulling the lanyard).

    Once it was upright, we boarded and I started it. It started up without too much difficulty and it idled fine, but it was and continues to be VERY sluggish when you open the throttle. If you open it quickly, it will stall. If you feather it, you can barely get it to accelerate.

    Here's the brain buster. If you pull the choke for just a second and let it go while you are opening the throttle, it runs PERFECT! You can run at WOT and it's like nothing is wrong. Once you get it past the "dead zone" (with help from the choke) it will run great and strong at 50+MPH at 6200RPM with no issues. If you let it come back to idle again, it's sluggish.

    I also noticed if you try to accelerate while turning left or right, after a few seconds, it accelerates fine, but it will not accelerate in a straight line without one of these three actions (pull the choke and release, turn left, or turn right).

    I pulled the plugs before leaving the lake and before playing with it some more and they look great....tan, not wet, not fouled, etc. There was hardly any water in the hull from the inversion.

    Anybody have any idea what could cause this???



  2. #2
    Do you recall which direction you tipped the machine back over? You're suppose to turn it right, or clockwise, to prevent water from the exhaust from getting into the engine.

    Im not sure enough past there to provide additional speculation. I battled with a SL that would run like garbage unless you pump the choke for years... Never found a solution.

  3. #3
    way2much2do's Avatar
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    Looking at the machine from the rear, I flipped it clockwise. I'm pretty sure that's the way the sticker on the back shows you to rotate it.

    Any other ideas? This is a strange one. I've had this machine for 3 years and it's been flawless. I'd like to keep it that way.

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Is there any water in the gas tank?

    Did you check the water seperator?

    Might not be a bad isea to inspect the carbs for signs of water inside the carbs.

  5. #5
    way2much2do's Avatar
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    Any body think there could be air trapped in the fuel system somewhere from running upside down for 3-5 seconds? I can't understand why if you turn left or right, or if you quickly pull and immediately release the choke the problem goes away. Could there be an air bubble somewhere? I checked plugs again, checked compression (130psi, 125psi, 128psi) and confirmed spark with all three wires and each of the plugs. Everything looks OK. I pulled the fuel strainer. It was full. I didn't see any evidence of water in it, but mine is the style that doesn't have the float in it. I checked all lines for kinks.

    Pulling and releasing the choke for a second when you open the throttle makes me think it is lean, but it acts like it's rich. If you pull the choke for more than just a fraction of a second, it will stall, so I don't think it's lean. If so, it's only during the transition between idle and WOT. I think pulling the choke may provide more vacuum to help pull fuel in? I don't know enough about these carburetors to understand if this makes sense or not.

    Anybody?

    Xlint: Thanks for chiming in. I've had the carbs and intake off this thing before when I upgraded the fuel pump, but I've never taken these carbs apart. What would be the procedure to check for water? Would it involve a complete disassembly? Is that difficult? Would I need new gaskets? Tonight I double checked my gas cap because I knew a batch of these machines had issues with them leaking, but it had presssure in it from yesterday's ride, so I think it's sealed good and I don't think I got any water in the fuel.

    Any other ideas?????

  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Look at post #5 for your turning sloutions.

    http://www.greenhulk.net/forums/show...-Engines-Carbs

    The carbs are pretty easy to do, no gaskets needed except the carb base gaskets. You can make your own from a roll of gasket material for $5.

    If the ski was upside down, any water in the water seperator would have gotten in the carbs since water is heavier than gas, it would have fallen to the hoses up-side down.

    For that same reason, water inside the carbs can clog a pilot jet, and not allow the fuel pass through the jet.

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    The inversion could have dislodged some gunk in the tank or elsewhere in the fuel system, which then made its way to the carbs.

    Be sure to check the pulse hose to the fuel pump for liquid.

  8. #8
    way2much2do's Avatar
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    AWESOME. Now I've got all the experts working on this one. Thanks a lot guys!!!!! It's really great to hear from you all again.


    Quote Originally Posted by xlint89 View Post
    Look at post #5 for your turning sloutions.

    http://www.greenhulk.net/forums/show...-Engines-Carbs

    The carbs are pretty easy to do, no gaskets needed except the carb base gaskets. You can make your own from a roll of gasket material for $5.

    If the ski was upside down, any water in the water seperator would have gotten in the carbs since water is heavier than gas, it would have fallen to the hoses up-side down.

    For that same reason, water inside the carbs can clog a pilot jet, and not allow the fuel pass through the jet.
    Interesting. Before taking it out yesterday, I removed, drained, and re-installed the separator/strainer and let the pump refill it when the engine was running. I watched it fill back up to make sure everything was OK before leaving for the lake. The rest of the ride was very uneventful and can't believe there was any other opportunity to get water in there (other than the inversion), unless it came from the tank from condensation over the winter. I do store my skis with the tanks totally full and I use stabil religously. I'll check out the post you referenced. Thanks Xlint!

    Quote Originally Posted by K447 View Post
    The inversion could have dislodged some gunk in the tank or elsewhere in the fuel system, which then made its way to the carbs.

    Be sure to check the pulse hose to the fuel pump for liquid.
    The upside down gunk theory makes sense. So, if we take this path as a possible cause, would it be possible to get gunk in the circuit that takes you from idle to WOT, but WITHOUT affecting either idle or WOT? As I said, it idles fine and once you get through the dead spot and get the RPM up, it runs GREAT. And, would it also make sense that if that "intermediate" circuit had gunk in it, would pulling the choke for a second to provide a little bit of "rich" to get through that make sense? Also, would turning explain it (maybe the gunk or water is moving around)? Just trying to reason it out.


    UPDATE: I just read the post Xlint referenced, and I'm not sure this applies. The ski runs better when turning left or right, but that link says "hard turns." These turns are not even close to hard. I'm doing this from a dead stop, turning the jet while trying to get it to accelerate - which it will barely do. If I turn the jet while trying to get it to accelerate, it will after a few second delay. If I don't turn the jet, it won't accelerate unless I pull the choke and release.

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by way2much2do View Post


    The upside down gunk theory makes sense. So, if we take this path as a possible cause, would it be possible to get gunk in the circuit that takes you from idle to WOT, but WITHOUT affecting either idle or WOT? As I said, it idles fine and once you get through the dead spot and get the RPM up, it runs GREAT. And, would it also make sense that if that "intermediate" circuit had gunk in it, would pulling the choke for a second to provide a little bit of "rich" to get through that make sense? Also, would turning explain it (maybe the gunk or water is moving around)? Just trying to reason it out.


    .
    Post #7 is the Mikuni manual. It will help you understand the answers to your questions.
    http://www.greenhulk.net/forums/show...uji-Carbureted

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by way2much2do View Post
    ... I'm doing this from a dead stop, turning the jet while trying to get it to accelerate - which it will barely do.

    If I turn the jet while trying to get it to accelerate, it will after a few second delay.

    If I don't turn the jet, it won't accelerate unless I pull the choke and release.
    It sounds like the engine needs a reduced impeller load to allow it to rev just a little higher. At some point, the increased RPM (and increased air flow into the engine) is allowing the carburetor to deliver fuel through a higher speed jet, and away you go.

    Turning can allow just a little jet pump ventilation or impeller cavitation, which reduces the drag on the impeller. Reduced drag means the RPM will rise.

    Something is causing the carburetor to not deliver enough fuel when you squeeze the throttle, OR something is preventing the engine from using that fuel.

    The fact that applying the choke also overcomes the problem leads us back to the carburetors. Something is limiting the carburetors ability to deliver fuel when the throttle is opened up at low RPM.

    Opening the throttle at low RPM is a very sensitive aspect of carb operation. Air flow volume and velocity are low because the RPM is low, despite the wide open throttle. Engine vacuum is low because the throttle plates are open. So the carb needs to flow more fuel to match the added (but slow moving) air flow, yet the 'signal' to do so is not strong. Every carb setting and function related to the low speed and transition circuits needs to be perfect.

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