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Thread: Failed Ignition Circuit on Rotax 912SP

  1. #21

    Failed Ignition Circuit on Rotax 912SP

    Mike Hallam wrote: Chris,

    I assume you had already twigged that your 50 rpm drop intermittently points to one ignition cutting out every now and then ?

    Shurely a hidden make break of one of the many wires inside the insulation or similar. The very Devil to chase down.

    As for your engineers cleaning 'points' ?

    Again there are no ignition points, whatever they told you. Unless you meant any plug in or earth clamp connections in the ignition solid wiring were called 'point' for checking any possible poor contact/connection ??

    mike hallam (912)
    Hi Mike - we are not so dodgy as to have told Chris we had cleaned the points! - but we have cleaned the pins in the connector plugs and surveyed for 'elastic wires' and obvious insulator damage etc. The fault of course is never manifest once bought in for check.. After this it was fine for a few weeks, but has since happened to Chris again.

    We did advise Chris to to cycle the mags immediately if it happened again to see if one was failing - and he did that . But it just mag checked with small smooth drop as normal.

    The units have also been checked on the ground cold - and both work.

    So it doesn't seem to fit the classical failure mode of the modules. It may be something else entirely. Like all very intermittent occasional faults ( especially ones that just cause a tiny rev drop like this) they can be very difficult to track down until the fault develops into something that manifests itself for a long enough period so we can see it and work out which bit is not working.

    Chris is keen to send units to Carmo anyway.

    Paul

  2. #22

    Failed Ignition Circuit on Rotax 912SP

    If it were mine I would be checking that the carb heat system is working correctly.

    Laurie (2)

  3. #23

    Failed Ignition Circuit on Rotax 912SP

    Another possible problem could be a worn earth wire insulation causing an intermittent drop but would need checked running each circuit individually to see which one and would show more than 50 rpm drop.The symptoms point to an earthing fault either wiring or Switches can you borrow a set of cdi units and change them individually to rule them out. I would still be looking at earthing faults primarily.

  4. #24

    Failed Ignition Circuit on Rotax 912SP

    Just to be clear. The 'classic' fault is highly dependent on revs and module temperature. At cranking revs, and low temperatures, there is no spark. Having got up to idle revs, there's usually no problem. Equally, warming the modules may restore a spark at cranking revs. When one module becomes marginal, it is usually masked because the other module allows the engine to be started and, once running, a mag check shows the marginal module to be working normally. I suspect attempting to start with one or other mag switched off might flag up a failing mag before both fail. However, my failing memory banks seem to vaguely remember advice not to start on one mag (perhaps someone can remind me?).
    Dave

  5. #25
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    Failed Ignition Circuit on Rotax 912SP

    Interesting read,I think I've got the dreaded wire broken somewhere lower plugs on 1and3 not sparking

  6. #26
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    Failed Ignition Circuit on Rotax 912SP

    Sounds more like a coil

  7. #27
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    Failed Ignition Circuit on Rotax 912SP

    Ok red wire from stator just stretchy insulation and one strand of wire left ,repaired that and a plug ( not very old) randomly missfiring,ran perfectly,have spent a few days scratching my head over this one,sorted now,thanks for the posts which got me on the right track

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