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Ignition checks

in 912 / 914 Technical Questions 11 years ago
I have a skyranger with 912s that I bought last year, that had a prop strike, and sat for 5 years. I've had the gearbox checked and certified ok, and had a crank runout done at 0 runout . It starts easily, and seems to run alright. I can't seem to run it up over 4000 rpm's when it runs rough. It seems to idle fine, but with a deep mellow kind of a vibration. When I flip the ignition switches to test the modules, the right switch doesn't effect the engine but very little. When I flip the left switch, there is a huge difference in sound and rpm's. we have switched the plugs on both sides of the modules to test the wires and mods. Even switched the plugs! The problem remains the same oN the left switch. The carbs are in sinc at idle and up to 3000rpms but change above that. Found out today that the previous owner/builder had the same issue! My A&P is baffled, and so am I. What should we look for?

  • Re: Ignition checks

    by » 11 years ago

    Sounds lean, change the needles to the next richer setting and then try it.
      
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  • Re: Ignition checks

    by » 11 years ago

    It might be lean with an air leak caused from the incident? Moving the needle may tell part of the story if it does better and has the needle ever been moved?

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: Ignition checks

    by » 11 years ago

    Carbs have just been rebuilt by an A&P, who is rotax qualified, not the same one i am working with now. The one thing that is baffling us so badly, is this, if the A modul controls the top plugs of 1&2, and bottom plugs of 3&4, and the B modul controls the bottom plugs of 1&2, and top plugs of 3&4, why would it always be the same scenario, if you flip the left switch even after you switch modules, and both mods and plugs are good? On the right switch the engine rpm's drop very little, my guess less than 30 rpm's, and when we flip the left switch it drops a good 300plus rpm's almost enough that you think it is going to stall. If it was the carbs you would think it would react the same on both switches, since each mod can run the engine by itself.

    I'm also wondering, I noticed by accident that the choke can rotate 360'. Could it possibly be that one choke could be 180' out, and is operating opposite of the other?
      
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  • Re: Ignition checks

    by » 11 years ago

    Hi David,

    The chokes could be in 180 out. Look for the little punch mark on the end of the choke shaft. It should be facing the intake side of the carb or what looks like a tube molded into the choke body. If the punch mark is facing the other way then there may be your issue, but I would think starting may be harder too. If you have switched ignition modules and the problem stays on the same switch then your problem if electrical is after the ignition modules.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: Ignition checks

    by » 11 years ago

    I checked the chokes and made sure that they were pointed in the right direction. No change ! Put a timing light to each of the plug wires, they seem to be firing the way they should according to the way I would think they should, with switches on or off! Just can't figure out the serious drop in rpm's when I flip the left kill switch for the mods checks. The one thing holding up my annual inspection.
      
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