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Thread: Igintion Issue

  1. #1
    Agfoxflyer's Avatar
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    Default Igintion Issue

    I have a Series 5 with a 912ULS. A few weeks ago I ran up the engine and did ignition check. Ran fine with ignition A grounded out. Switched and ran real rough on A alone. It runs and sounds fine with both ignitions on. Mechanic has checked both ignition modules, and coils. I have checked all spark plug wires. Someone suggested it might be a bad connection on the ignition switch for A. Will check that out next time at airport. Question, if an ignition module is bad or going bad, does it run at all? Any other ideas would be appreciated. Need to go flying.
    David E.
    Woodstock, Georgia
    N97DE S5 TD Flying

    N97KE RV-9A Sold
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  2. #2
    Senior Member
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    Default Re: Igintion Issue

    I suggest VERY carefully checking the ground wires on both modules.

  3. #3
    Senior Member Dave S's Avatar
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    Default Re: Igintion Issue

    I'd second the ground wire check. The original 912ULS has a separate ground wire for each module going to the intake manifold each held by a separate screw. I believe, where the manifolds are switched right to left to make room for the oil tank, on some S5s one of the mods with the manifold switch hooked both ground wires to a bracket and the bracket to the manifold with a single screw due to the shortness of the ground leads - basically combining the separate grounds through a single point. Might be worth a check on the module grounds. But - your mileage may vary.........could certainly be something else too....
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  4. #4
    kitfoxnick's Avatar
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    Default Re: Igintion Issue

    I second the others advice. Breaks in the ground wires can be hard to find sometimes. I find the easiest way to find the culprit wire. Is to stick a sewing pin through the wire insulation on the coil ground wires, and measure reisestance with a multimeter.
    Nick W
    IV 1200
    912Ul
    Warp Taper Tip

  5. #5
    Senior Member HighWing's Avatar
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    Default Re: Igintion Issue

    I have had similar symptoms on my 912 UL on cold start after sitting for a while. Then after changing plugs, all good again. My take is that my infrequent flying with Avgas to avoid the unleaded's degradation on sitting did a number on the plugs.
    Lowell Fitt
    Goodyear, AZ


    My You Tube Channel

  6. #6
    Super Moderator Av8r3400's Avatar
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    Default Re: Igintion Issue

    Another thing that I have discovered. These ignition units are not very powerful. I gap my NGK plugs (per Hal Stockman's recommendation) to .020-.024". I have found their performance is better than the .028-.032" recommended by Rotax.

    Be sure to at least check them before installing. I have seen new plugs with up to .040" gap in the box.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  7. #7
    Senior Member Dave S's Avatar
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    Default Re: Igintion Issue

    Larry,

    I have thought about smaller gaps for the plugs on the ULS; but, have always gapped mine at the tight end of the Rotax recommendation at 0.028".

    Considering your experience with smaller gaps; have you observed this to be beneficial over the entire spectrum of operations? What have you noticed on specific conditions like cold start, low RPM, full power (I would think it would insure better ignition under WOT for sure) and ranges between idle and full power. Do you get better performance with our cold ambient temps up here in the northern tier?

    I tend to reuse plugs that are in good shape; and, include a resistance test along with cleaning and visual evaluation - on occasion I have found a plug with infinite resistance under the meter which still fires well which indicates to me that the carbon resistor is cracked - those get tossed. I need to checking resistance on new plugs also - at least on other engines, new plugs are not always right I have found - hence my choice to reuse "road tested" ones if they are otherwise OK. Any thoughts on cleaning and reusing plugs from your experience?
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  8. #8
    Senior Member jrevens's Avatar
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    Default Re: Igintion Issue

    According to the maintenance manual for my 912 ULS, the gap is supposed to be .023 - .027".
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  9. #9
    Administrator DesertFox4's Avatar
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    Default Re: Igintion Issue

    I used .023 to .024 for years with better results than the wider gapping. I did not have the high torque starter or soft start and the closer gap helped on starts on mornings with 50 degree temps or colder.
    Also used 100% 100 LL Av Gas with Decalin additive and experienced no fowling between 100 hour plug changes.


    DesertFox4
    Admin.
    7 Super Sport
    912 ULS Tri-gear


  10. #10
    Super Moderator Av8r3400's Avatar
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    Default Re: Igintion Issue

    Dave - I found the engine to run smoother across the rpm spectrum. Cold starting seems to be easier, too.

    I buy 8 new spark plugs every year. For $16, this is cheap maintenance. Cleaning and reusing these plugs isn't worth the effort, IMO.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

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