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Thread: HELP slt 780

  1. #1

    HELP slt 780

    I took it out today. Last week it ran like crap, I thought it was a poorly adjusted carb, so I took it back. He ramped up the idle speed.

    Anyway, I took it back out. Ran fine for about 2 minutes, then it fell flat on it its face. Won't go over 10mph and rpm <3500. same as last week.

    Pulled the plugs. Aha, the front cylinder has a film of fuel and oil on the plug but not black whatsoever. the middle and back cylinder are black. If I crank it and let it idle, pulling the front plug wire does nothing to the rpms. The middle and back cylinder plug wires will kill the engine when pulled. obviously, it's running on the back 2 cylinders only.

    The front carb spits a little fuel out when you pop the throttle. In fact, it's getting fuel all over the place after a while. I'm getting fire to the plug; I can see a spark at the electrode.

    Now, what is the problem? No limp mode indicators (fuel, oil, voltage, etc seem to be fine.) Is it a blockage in the carb (some gas is getting in, though), or is it a bad plug wire or sensor?

    also, compression was tested previously. I don't know the #s, but the shop said it was fine.

    I don't want to spend a bunch of time and $$ on parts that are fine.

    thanks in advance.


  2. #2
    ph2ocraft's Avatar
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    If the front cylinder doesn't hit and you know you have spark, it's either fuel related, compression or indexing (which I doubt as you stated it ran good for 2 minutes).
    I would
    Check compression
    Check Indexing
    Pull carbs and check for crap internally
    Check reeds while the carbs are off
    Replace needle and seat while I'm there


    How are the lines?
    Crap in the tank?
    Water Intrusion?
    Pump condition?

  3. #3
    thanks for the quick reply. do you think it may be crap in the carb? I'm getting "some" fuel on the plug, but I don't know if this is enough. A lot spits out when the throttle is pressed. The cylinder doesn't get very hot, just "warm".

    I'll take the carb off and look. I hope it's that. It just threw me that fuel was on the plug. It seems (to me) that it would burn what little it received.

    thanks again.

  4. #4
    Moderator beerdart's Avatar
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    Quote Originally Posted by rbridges View Post
    thanks for the quick reply. do you think it may be crap in the carb? I'm getting "some" fuel on the plug, but I don't know if this is enough. A lot spits out when the throttle is pressed. Is the spiting back out of the carb? The cylinder doesn't get very hot, just "warm".

    I'll take the carb off and look. I hope it's that. It just threw me that fuel was on the plug. It seems (to me) that it would burn what little it received.

    thanks again.
    .

  5. #5
    ph2ocraft's Avatar
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    Quote Originally Posted by ph2ocraft View Post
    I would
    Check compression
    Check Indexing
    Pull carbs and check for crap internally
    Check reeds while the carbs are off
    Replace needle and seat while I'm there
    How are the lines?
    Crap in the tank?
    Water Intrusion?
    Pump condition?
    Check it all, you want to make sure the fuel system is free fron garbage.
    You want to make sure the reeds are in good shape due to the spitting of gas through the carbs.
    You should still make sure the engine compression is good just to know you have a decent engine to diagnose.
    Checking crank index can also be a sputtering, RPM issue.

    It may be overkill BUT why not make sure your engine is healthy and you're not pulling it apart again next week. Just my humble opinion before stroker the 15 year fry cook comes looking for me.

  6. #6

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    if you have wet plugs than you have a tune carbs issue , or crap compression or incorrect sprak plug gap ,

  7. #7
    found it (I hope). there is a broken reed. bottom center piece (of 6). would this cause the problems. everything else looked pretty clean in the carbs.

    btw, the spitting was out the carbs (into the filter area).

  8. #8
    Moderator beerdart's Avatar
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    A broken reed would cause all of the symptoms you have! It's all about suck and blow. The reeds are check valves.

  9. #9
    Quote Originally Posted by beerdart View Post
    A broken reed would cause all of the symptoms you have! It's all about suck and blow. The reeds are check valves.

    thanks for the response. you guys have been a tremendous help. definitely better than paying someone $60/hr to dig around the motor.

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