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Hi, all!

 

We have yet another "the engine is running rough" story to contribute.  We have to say that after reading some of the horror stories folks have lived we feel not so bad :-) but we really want to get this nailed.  Our 912ULS is about 8 years old with 1200 hours, and we've put on 1100+ of those in the last 7+ (wow!) years.

The carbs balance wonderfully, but we haven't torn everything apart looking for intake leaks, so we can't rule them out.  They've generally been good, the last time Lockwood serviced them they got a few new pieces and clean bills of health, and they aren't yet due for the next 200hr pass.  We did weigh the floats, and we're well within tolerance.  We tried the "choke test" and in general things seem fine; we couldn't spot any particular setting as way too lean or rich.  The stumbling is most noticeable in the midrange like the low 3000s, we'd say.

We've eliminated the stator by swapping the red wires around, and we've eliminated the ignition modules by swapping the "after" MOLEX connectors.  That should put us at the "A" wires & plugs, which is 1 & 2 top and 3 & 4 bottom. Unfortunately, the plugs don't look noticeably different compared to their friends; there isn't one that stands out.as an obvious problem.  The boots are all happy & flexible and well-attached to the ignition wires so far as we can tell.  Soooo ... we dig.  Our next step, tomorrow morning, will be to sequentially disconnect each plug and see if the mag check is the same kind of unhappy, figuring that if it is then that's the plug that isn't pulling its weight.

At this point, we think we'll need to dig into resistance checking.  We have the numbers from the MMH, but ... how do we check a given plug wire (in the boot, or pop it and poke the wire directly? and what about on the other end?) to confirm that it's good, and what measures (such as trimming back the wire and putting the boot on fresh, we read somewhere) should we take if it looks bad?  We're really hoping to not have to pull the coils pack and everything else, but it kinda feels like that's in our future :-/

Thanks in advance for any advice and direction!

D

  • Re: yet another "rough running" thread

    by » 2 weeks ago


    My wife, Jennifer, who also flies and works on our RV12, wants to know if I wrote this post.  I did not, but I could have.  Exact same problem, tried same solutions, months of frustration.  Finally solved it at the spark plug wire level.  Clip a quarter inch off the end of each wire, use dielectric grease, re-thread the caps, make sure the gaps are good, everything is snug, and see if that helps.  That’s what worked for us.  I wish you the best, my friend,  This one can drive you nuts.


  • Re: yet another "rough running" thread

    by » 2 weeks ago


    I had a problem with a random miss that was not bad enough to ground the plane but very annoying. It was hit and miss and I couldn't connect it to a mag side or anything else other than it would occur more around 4500 rpm where the engine ran a bit rougher. I did everything that you have checked with no positive results. Carbs, plugs, checking all wiring,nothing would solve it. My engine is a 2015 with1400 hours at the time. I had previously ordered plug wires and caps, bulk wire from Spruce and caps from K&S, about $80 for all. I really was putting it off because getting to the coils to replace the wire requires a bit of dis-assembly. In any case I did replace everything and have after 40 hours have not had a single miss.

    I had previously ordered new wires because I had a few that were too short to cut back. The K&S caps are superior to the Rotax or NGK ones which are impossible to find.


    Walt

    my blog; waltsrv12.com


  • Re: yet another "rough running" thread

    by » 2 weeks ago


    Thanks, Pete, and tell Jennifer that Laura (my "we" other half) says I'm real and not just your pen name ;-)  Glad to hear that trimming the ends is not a stupid idea, because we'd sure rather that than ripping apart the whole topside!

    Stay tuned.


  • Re: yet another "rough running" thread

    by » 2 weeks ago


    Thanks for the reply, Walt!  Good to know that there's hope.  If we do go to all of the effort to tear down the ignition system, we want more than just crossed fingers and blind hope on our side :-)  So, yeah, we'll be ready.

    Fingers crossed ...


  • Re: yet another "rough running" thread

    by » 2 weeks ago


    Stupid frickin' cookies and login timeout and NO WARNING and throwing away my post *sigh*  No, I don't have time to rewrite it properly before the next student gets here, so I'll just say
    - we trimmed (for those that can't find it like I couldn't, you cut off about 1/4" square across the end, preferably with something like flush-cut nippers, leaving no wire hanging out) our plug wires and liked the improvement on the suspect so much that we did all 8
    - THANK YOU to all for the help and advice :-)

    D & L


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