Kitfox Aircraft Stick and Rudder Stein Air Grove Aircraft TCW Technologies Dynon Avionics AeroLED MGL Avionics Leading Edge Airfoils Desser EarthX Batteries Garmin G3X Touch
Results 1 to 7 of 7

Thread: Fch

  1. #1

    Join Date
    Mar 2016
    Location
    Helena MT
    Posts
    5

    Default Fch

    I have a 912ULS in my Speedster.
    The ignition switch is key operated with off, left, right and start. On the last flight, on shut down, the off position would not shut down the engine. the RPM would drop to 500 then cycle back to 1000. It would continue to do this, so I had to shut off the fuel to stop the engine.
    I suspect the switch is gone bad. Am I on the right tract or could something else be causing the problem

  2. #2
    Senior Member Dave S's Avatar
    Join Date
    Oct 2008
    Location
    St Paul, MN
    Posts
    1,833

    Default Re: Fch

    FCH,

    Don't get too carried away and replace the switch just yet.

    The problem you describe is a classical P lead open - There are two wires running from the switch to the ignition modules - If one if these wires becomes disconnected; or, breaks, the problem you describe is exactly what will happen.

    When you turn the switch to off, the switch contacts will ground each of the two P leads shutting the ignition off. The switch can be checked with a multimeter to verify it is grounding; but, your problem is likely not the switch.

    Check the P leads for continuity and solid connection at the switch and at the modules. The P leads on the engine side are subject to vibration and can crack resulting in a open condition. Wires can sometimes crack internally under the insulation. A good tug on the wires will usually find that. The screws on the switch can also come loose if not tight enough.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  3. #3
    Super Moderator Av8r3400's Avatar
    Join Date
    Jan 2009
    Location
    Merrill, WI
    Posts
    3,044

    Default Re: Fch

    This is a very common failure on Rotax 912 series engines.

    There has been much debate here on this, but LEAF has replace many faulty left-right-both switches due to their incompatibility with the CDI ignition. I trust their expertise.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  4. #4

    Join Date
    Mar 2016
    Location
    Helena MT
    Posts
    5

    Default Re: Fch

    Thanks for the info
    This Speedster is a 1993 model and has been working fine for over 1500 hrs.. I am going to do some double checking of the wires. I had one break several years ago.

  5. #5
    tommg13780's Avatar
    Join Date
    Nov 2008
    Location
    Guilford, NY
    Posts
    156

    Default Re: Fch

    After sitting 6 months during off season I had a kill switch malfunction. I went old school fix by eliminating the stake-on connector at the module and going twist and solder/encapsulated with 2 layers of heatshrink. This is the second time for this problem on 2 different 912's and I've only accumulated around 200 hours flying time total on both.

  6. #6

    Join Date
    Mar 2016
    Location
    Helena MT
    Posts
    5

    Default Re: Fch

    In checking the P lead wires I found one break under the insulation. Repaired it and checking the other P lead I found another area that the wire had broken all but one strand. Repaired it. Haven't had a chance to fly, but I run the engine and then turned it off with the switch and it worked OK.
    When I had a P lead break several years ago, when I turned off the switch the engine continued to run normally. This time when I turned off the switch the engine would cycle between 500 and 1000 RPM.
    I really zip tied the wires down so I hope they won't break again.
    Problem solved.

  7. #7
    Senior Member Slyfox's Avatar
    Join Date
    Dec 2008
    Location
    felts field, spokane
    Posts
    1,327

    Default Re: Fch

    I love mine on individual throw switches. the starter is on key, will change to push button some day.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •