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  1. #1
    TyCast's Avatar
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    Exclamation Erratic bogging behaviour. Causes? 1993 Polaris SL 650

    i took my 1993 Polaris SL 650 out today and had a headache pretty much the whole time.

    Last time i took it out, it was running perfect. I had just took the autocock out and it was running great. Thatt was last week.

    Then i took it out today, it started and ran, but then i noticed it couldnt throttle more than half way throttle. It would bog down more than half way till it sounded like it was going to die. So, i kept it at half throttle.

    Then, it would bog down then up then down again, in an erratic manner. A few times the engine actually died from bogging down too much. And it was hard to start again. Took several minutes of trying to start it.

    I took back to the dock and took the petcock (fuel selector) out. It seemed fine. It helped it run a little bit, but then a few minutes, same erratic pattern again. And the engine died a couple times.

    I suspect that water somehow got into the gas tank. There was a large rain downpour a couple days ago and its been getting colder lately. Condensation maybe? Water leak into the tank?

    Please help!

    Thanks,
    - TC
    Last edited by K447; 11-10-2013 at 08:32 PM.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    If the fuel is contaminated or has water, you need to investigate and/or drain the tank.

    When you say bogging down, was the engine missing, like it was starved for fuel?

  3. #3
    TyCast's Avatar
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    description

    So, the bogging was like this roller coaster effect on the RPM. It would be running fine, then the RPM would slow down, so i would let up on the throttle, then it would accelerate to full power for a few moments, then the it would bog and the RPMs would slow down in a cycling manner. At some point, it did sound like it was missing the fires when it was near idle speed. It would "pa-PA! Pa-pa-PA, pa...pa", like the fuel line was being turn off then on, then off, etc.

    Would water-tainted fuel cause that random up-down RPM cycling? Could it be an electrical problem maybe?

    i wanna siphon some gas out tomorrow. Water sinks in gasoline as i remember.

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    If there is water in the fuel tank, you really should drain the tank completely, then wipe it down inside and dry it out.

    If there is dirt or sediment in the bottom, clean that out too. Inspect the fuel pickup for clogs or dirt. The fuel tank needs to be 100% clean inside.

    Inspect the fuel filler neck and gas cap. Look for hairline cracks, bad seals. It needs to be 100% watertight. If needed, you can install a newer generation Polaris or SeaDoo gas filler neck and cap.

    Every hose and seal on the fuel tank must be good.

  5. #5
    TyCast's Avatar
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    I also found this quote from you K44 in another thread:

    "Clean and check the fuel selector valve - must not have air leaks under suction. You may need to take it apart and rebuild it - new o-ring, lightly greased."

    Would an air leak in the fuel selector value cause inconsistent fuel delievery?

    I will check on my tank tomorrow. First, i will check if the fuel has water in it using a clear gas jar.

    And you said you can "wipe the inside"? How is this done? Does the tank top half separate from the bottom?

    I really think its the selector value. Last ride, last week, i had to move the selector value to inbetween "on" and "off" to make the ski run normal. Im thinking removing the autocock is messing with the fuel select value, which i didnt fix, and is still the original 1993 condition. I plan on removing the fuel select value then replacing the one o-ring in there.

    But i also believe it could be water in the tank. I will know more tomorrow.

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    'Wipe inside' means a cloth and a stick, or whatever it takes, to get the tank clean inside. It may just need washing out with some cleaner, good rinse, drain and air dry in the sun.

    Sometimes it is better to remove the tank from the hull so you can really work on it.

    If the old fuel selector is in poor condition or you do not trust the repair, new ones are available

  7. #7
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    Keith is correct about checking the fuel system from front to back. Even if it's not your problem, you very well may prevent a future issue. Being a 1993 SL 650, I believe your fuel pickups are the hose and screen type, meaning that those fuel hoses have been sitting in that tank for 20 yrs now. They can crack, break, fall off, and just plain get blocked up. (the screen part) Worth looking at.
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  8. #8
    TyCast's Avatar
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    I actually replaced the old fuel lines inside the tank. They were rotting apart. i didnt replace the black fuel lines thou, just the 2 that go into the tank for ON and RES.

    Im going to do some investigating today and I will report back.

  9. #9
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    i believe I have found the problem, at least one of the problems.

    First, i will explain what i did.

    I first looked at the fuel in the tank. I took the 2 gas lines out of the tank and emptied them into a clear glass jar. There was just fuel in the lines to fill an inch inside the jar. I left it and came back 20mins later. No fuel/water seperation. There was this cool dropplet effect when the fuel dropplet met with the glass jar, it would bounce up and down.

    Anyway, besides the point, it wasnt water in the fuel.

    So next, i took the spark plugs off and believe to have found the main problem. Cylinders 1 and 2 had this oily black tar stuff on the threads of the plug, a similiar substance found on the inside the down stem of a well-used water bong.

    But cyclinder 3 (the one nearest to the bow) was totally different. It had a whitish/grayish watery substance on the plug. And when i cleaned it with a paper towel, it wiped clean and looked like a brand-new plug.

    Is it a water leak into that cylinder?

    How do i fix it?

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Water sitting in the bottom of the fuel tank may or may not also be in the pickup tubes. As you said, water sits at the lowest point in a static container. When you are out riding, the water (if there is any) would be sloshing around under the fuel. Sometimes it would be near the fuel pickup, sometimes not.

    Tip: Engine cylinders are numbered from the front of the hull. So you have a potential water leak into cylinder 1, also known as the MAG cylinder (short for Magneto).

    You could seal off and pressure test the water jacket. Probably easier and more conclusive is to simply remove the cylinder head and visually inspect. Often a failed gasket is immediately apparent once you look at it.

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