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Engine Roughness, Mag Drop

in General Tech Discussion 12 years ago
I have the 100 hp 912 ULS engine and with soft start. When I do a mag check, and shut down switch #1 hooked to the SS model the engine runs smooth, but when I kill switch #2 the engine runs rough with extra rpm drop. I've pulled plugs on modules to check to see if there was a bad connection, no change. New o-rings in carbs and jets cleaned and spark plugs cleaned. Also two front cylinders seem to be burning a little rich. Any ideas as to what the problem might be?

  • Re: Engine Roughness, Mag Drop

    by » 12 years ago

    Ralph,

    Couple of questions. At what speed are you checking the mags? Are you using the rotax ss modules or the bullyhawk type which connects to only one ignition module? If it is the Bullyhawk type, you might try disconnecting the ss module and see if the mag drop problem still exists. If it does, the ss module is not the problem. If you have the Rotax factory type ignition modules with ss. You can try reversing the module positions (a to b and b to a). if the kill switch problem reverses, it could be the module. If it stays the same, it is probably in the wiring somewhere.

    It sounds like the problem is in the circuit controlled by the #1 switch since the engine continues to run smoothly with that circuit shut off. You might even try reversing the plugs to eliminate them as a problem. Go top plugs to bottom and bottom to top and see if the problem reverses.

    Hope some of this helps.

    Bill.
    Thank you said by: YEN NIEN YU
      
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  • Re: Engine Roughness, Mag Drop

    by » 12 years ago

    I've tried and done mag checks at different rpm settings with same result. SS is Bullyhawk type. Will try your suggestions, "thank you very much" and repost results soon.
      
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  • Re: Engine Roughness, Mag Drop

    by » 12 years ago

    I reversed the module positions (a to b and b to a) and it did reverse the problem. I'm going to run the plane for a bit to see if the plugs that show signs of carbon also change to see if confirm it's connected. I didn't disconnect the Soft Start because you can hear that it is working properly on start up of the engine and it was on the side that was running smooth.
      
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  • Re: Engine Roughness, Mag Drop

    by » 12 years ago

    Ralph,

    You probably already know this so please don't be offended, but it can be confusing sometimes.

    If you kill one mag and the engine runs smoothly at a lower speed, the mag you killed is the bad one, not the one that is still running. You still might want to disconnect the soft start just to be sure its not causing a problem.

    Bill.
      
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  • Re: Engine Roughness, Mag Drop

    by » 12 years ago

    I understood that and the @2 switch is the one opposite the Soft Start Mag. It only takes a sec, so I'll do it just the same to make sure. My fear is to purchase a Module only to find out its something else. It might be worth sending the mags in to have them tested if that's possible.
      
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