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Thread: Ruff running on one mag(elect module) on my 912s

  1. #1

    Join Date
    Dec 2011
    Location
    abbeville SC
    Posts
    1

    Ruff running on one mag(elect module) on my 912s

    I have a highlander with a 912s, 500hrs TT.
    Started having problem with engine running rough on one mag(module)and on cold start dead on that mag untill abt 3min warm up then works but rough compaired to opposite mag, about 100 rpm def on mag test at 4K.
    I have a bully hawk soft start module installed and when disconnected I have the same problem.
    Bully hawk people said it might be the module pickup coil is not set right.
    Has anyone adjusted these pickups and can give me heads up on difficulty?
    plugs have been gapped and all show good color.
    Bob

  2. #2
    Barnstorm's Avatar
    Join Date
    Nov 2011
    Location
    Cincinnati, Ohio
    Posts
    77
    I know this sounds strange and impossible..

    Use a digital carb sync to sync your carbs and make sure your engine is up to running temp.

    I have seen cold engines and off-sync carbs cause rough running on one mag.

    .
    "The exhilaration of flying is too keen, the pleasure too great, for it to be neglected as a sport" Orville Wright
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  3. #3

    Same Problem

    I'm having the same problem on my Rotax 912ULS with Bullhawk SS, did you discover what the problem is???


    Quote Originally Posted by rubobrun View Post
    I have a highlander with a 912s, 500hrs TT.
    Started having problem with engine running rough on one mag(module)and on cold start dead on that mag untill abt 3min warm up then works but rough compaired to opposite mag, about 100 rpm def on mag test at 4K.
    I have a bully hawk soft start module installed and when disconnected I have the same problem.
    Bully hawk people said it might be the module pickup coil is not set right.
    Has anyone adjusted these pickups and can give me heads up on difficulty?
    plugs have been gapped and all show good color.
    Bob

  4. #4

    Join Date
    Sep 2012
    Location
    New York
    Posts
    1

    Mag help and troubleshooting

    Hello everyone. First I'm an A&P mechanic with an approved Rotax certification on the 912 series engine. With that being said lets get to the business. Assuming that the problem you gentleman have is with the ignition system here are a couple of possible faulty components and some simple troubleshooting procedures you can use to help diagnose your fault. 1. Let's assume the carbs are both synced properly. 2. Check that all of your ignition cables are securely attached to your spark plug connector. There is a specific pull off force for the spark plug cable cap from the spark plugs. The minimum pull off force is 30N (newtons) or 265in/lbs. 3. If the fault persist your spark plugs maybe be bad or out of tolerance. The minimum gap for new plugs is .6" and max gap of a new plug is .7 new. I try to keep my gap as tight as possible or close to .6" the plugs can wear to .9" and at this point .9" the plugs are toast. 4. Let's get to some tougher stuff. Let say you suspect either an ignition module or an ignition coil. Your solution will be either a $1000 ignition module or a $300 ignition coil. That's a big difference in repair bill if you ask me. So here is a quick tip to determine which part is bad. These engines are redundant so I would swap parts A system to B system. 5. The trigger coils can sometimes be a problem and may also need adjustment. This solution may just be the best and only cost 1 labor hour or two to your favorite A&P or light sport repairmen with a rotax maintenance certification. Additionally the fault everyone is experiencing seems to iminate from an out of tolerance trigger cool. These faults show there symptom such as duff running and larger than normal mag drops 300 +RPM. These are basic trouble shooting technics and I hope they help. If anyone has any specific questions feel free to pm me and I will reply promptly.

  5. #5

    Join Date
    Aug 2011
    Location
    FA40
    Posts
    425
    "I try to keep my gap as tight as possible or close to .6..." that's an old-timer trick for making reluctant engines with Kettering ignitions easier to start in cold weather. close-gapped plugs start the engine easier, but aren't always optimum for cruise power and above. those old-timers used to gap plugs wide for high-power operations. of course, today's ignition systems are all CAD designed and computer controlled, so experience and common sense are out of date. your choice.

    "the plugs can wear to .9" and at this point .9" the plugs are toast" or, you could clean, file, and regap them then reinstall with a new crush washer. a professional mechanic does toss them, of course, because it's cheaper for the customer than his labor to re-use them. but the plugs aren't toast.

    "...so I would swap parts A system to B system..." meaning, if one is going to troubleshoot with parts, use parts one already owns. good advice! well, until i mess up both parts switching them. but that's another story.

    "...only cost 1 labor hour or two to your favorite A&P or light sport repairmen with a rotax maintenance certification." or, if the aircraft is experimental, do it yourself.

    if you aren't sure what you're doing, find someone who is!

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