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Skandic 503 Troubleshooting a dead hole

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  • Skandic 503 Troubleshooting a dead hole

    '94 503LTR, burned up a piston hauling firewood on old gas last year. OH'd the bad cylinder/piston with new and reassembled. Ran strong right on start up.
    This season, the newly OH'd cylinder has compression, fuel and spark but doesn't fire. Once the rpm gets high enough (3/4 throttle +) the cylinder comes to life. Thought it might be a spark issue (higher rpm, hotter spark) But am not sure a stator works like that.
    It has the three basic components and no go. Anyone want to take a stab at this? I have built a number of auto/aircraft engines but this is the first two-stroke I've ever done. The spark is not a bright blue but I've seen much worse fire. The compression was not checked with a gauge but seems equal to the other cylinder. I completely disasembled the carb and cleaned every orifice and passage. Bowl looked clean and floats were OK.
    While the engine is running, I can pull the carb slide completely out with no effect. I can see the fuel running through the carb and the plug is wet.
    BTW, this is a cabin machine and hasn't been out of the bush in almost 10 years.

  • #2
    Sounds like a stator or CDI problem, or maybe something simple like a bad spark plug cap.

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    • #3
      Stator or CDI should effect both cylinders. On a one cylinder spark issue it's usually the cap or the coil. It's been a while for me on a 503, but I think it has a coil for each cylinder that then hook into the CDI then the Stator.
      Bunny Boots and Bearcats: Utility Sled Mayhem

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      • #4
        the coils on those break down in slow increments before they finally fail.. new plugs, new coils and wires too...


        also keep in mind a plug laying on the engine cover may spark with no Resistance on it.. however one may go bad under pressure. or while under compression as the case may be.

        your stator works or it dont.. you may pull your recoil off and take some breaklean to it and wash any crude out... but dont screw with it, they are a bear to retime.

        most 2 stroke top end jobs should be done in unison to keep balance on the crank as well. pistons vary in weight by lot # and then you still may be off a few grams, which leads to uneven wear, premature bearing failure and rebuilds done more often.
        "If you are on a continuous search to be offended, you will always find what you are looking for; even when it isn't there."

        meet on face book here

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        • #5
          Yeah, I thought of that after the fact Vince. May still do that, hopefully will wait for summer as the machine shed gets cold.
          As far as the spark on the dead cylinder, I looked at that during the intial diagnosis. I swapped the plug leads from the dead hole to the live and it fired the good cylinder right up which suprised me. I assumed the spark would have been timed to the exact firing order. Makes me think that during the Top end OH, I swapped the leads but the lead length wouldn't have allowed that.

          I tried to get out to the cabin this weekend but the wind was gusting over 70 at home and it was a little too risky of a flight..
          I guess I'll mull this over some more during the week.

          Comment


          • #6
            Have you checked the crank seals?
            Spray some starting fluid on them and see if that affects it.
            Sometimes this can affect starting and running.

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            • #7
              Originally posted by Badriverman View Post
              Have you checked the crank seals?
              Spray some starting fluid on them and see if that affects it.
              Sometimes this can affect starting and running.
              a leak in the cylinder base gasket may do the same thing
              "If you are on a continuous search to be offended, you will always find what you are looking for; even when it isn't there."

              meet on face book here

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              • #8
                You've got a bad crankshaft seal, probably on the PTO side. John

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                • #9
                  Originally posted by Older Snowmachine Repair View Post
                  You've got a bad crankshaft seal, probably on the PTO side. John
                  Is this John @ 90s and older?
                  I don't mean to sound bitter, cold, or cruel, but I am, so that's how it comes out.
                  Bill Hicks

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