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Thread: 912UL Issues

  1. #1

    Join Date
    Jun 2013
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    Spokane, Wa
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    Default 912UL Issues

    Hey guys- looking for some opinions. I just bought my 94 model IV, when I got it seemed to run rough, I chalked most of that up to sitting( I think it has been sitting most of its life imo) fixed a few squawks, changed plugs, rebuilt carbs with new gaskets and needles, checked float level, synced. The problem is this- at idle to 2500 the engine shakes violently and the gearbox is making lots of noise. It shakes so much the right carb pukes a little fuel from the vent line. From 2500 up it smoothes out, pulls cleanly all the way to 5250. I have triple checked the jets, sync is right on from 1400 and up. I think there is something wrong with the gearbox- seems weird it would be bad at 145 hours Any Rotax techs close to Spokane/CDA? Any input would be appreciated.

    Thanks,

    Scott

  2. #2
    Senior Member Slyfox's Avatar
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    Default Re: 912UL Issues

    when I get this I know it's the middle range jet circuit. If you have seen the circuit you would understand. it goes through the jet and comes out in front of the filter or opening of the carb. the vent hole is about .030 real small. My advice is to remove the carb bowl, take this jet out and take some carb cleaner in a can or brake cleaner and squirt up into the opening for the jet and when you see a small stream come out the carb at the filter area you know you got it cleaned out, remove the filter of course. mine generally has a bunch of brown junk come out at first. than take some shop air and do a round about on the circuit, put it back together and should be much better. the jet is between main jet and the front of the carb twards the front of the engine.

  3. #3
    Super Moderator Av8r3400's Avatar
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    Default Re: 912UL Issues

    I've been noticing the same thing lately, only it seems to be intermittent. Runs smooth sometimes and other times it runs real rough at low rpm...

    Been very frustrating. I'll try this technique. Thanks!
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  4. #4
    Senior Member kmach's Avatar
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    Cupar, SK, Canada CLC4 Loon Creek Airfield
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    Default Re: 912UL Issues

    Hi, To me it sounds like your sync might be out. some Rotax people sync at 2500, some recommend and swear by doing it at 3000-3500 rpm. I have tried both and around 3000 works best for my setup .

    I recall my first syncs didn't work out and I have had the fuel exiting the carb overflow. retried the sync , with some trial and error and experience syncing is easy and definitely smooths idle and lower rpms out.
    Kevin,

    Kitfox Outback
    912 ULS
    Airmaster AP332CTFH-WWR70W
    Summit Aircraft Wheel Skis
    C-FOXW

  5. #5
    Senior Member
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    wilmington nc
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    Default Re: 912UL Issues

    hi guys, saw this a while back on a friends 912. syncsed the carbs, no help. rebuilt carbs, no help. installed new carbs, no help. after all that time and money it still ran so bad at low speed that we took the prop off so we could pull plug wires off while it was running to try and find the problem and lo and behold it ran great.
    called lockwood and told them what we were seeing and they said to send them the gear box to be checked out. turns out the dog gear was frozen to the shaft and was not cushioning the low rpm impulses from the motor as it was supposed to. much money later and a rebuilt drive it runs great. hope this helps

  6. #6

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    Jun 2013
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    Spokane, Wa
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    Default Re: 912UL Issues

    Jim Scott (Aircore Aviation) when I called him said the exact same thing. So I am pulling the gearbox and shipping it off. I will keep everyone updated.

    Thanks for all the input-

    Scott

  7. #7
    Senior Member SkyPirate's Avatar
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    Default Re: 912UL Issues

    this is also a common low rpm thing with the B box's on a 582 but its the spacers and springs on output shaft that is the culprit,..when you start getting allot of low rpm chatter out of the gear box,..time for rebuild

  8. #8

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    Default Re: 912UL Issues

    I thought I would post the end result on this so maybe it might help someone else along the line later on- It turned out to be the gearbox, sent it out to Jim Scott at Aircore Aviation in Arlington, (great guy and highly recommended) got it back in record time(would have been faster but parts were back ordered) bolted it back up, retorqued everything, safety wired, fired up and she runs smooooth. no puking carb, no weird noises. And my plane only has 145 hours on it- so go figure.

  9. #9
    Super Moderator Av8r3400's Avatar
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    Default Re: 912UL Issues

    I have the parts in hand to do mine now too. I hope it works as well.

    As a side note, what prop do you have? I have a 3-blade 68" warp with tapered nickel leading edges. 450 hours tt on the motor.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  10. #10
    Senior Member Slyfox's Avatar
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    Default Re: 912UL Issues

    fantastic. when i left the airport last night I saw you going out the gate with your airplane in tow. I take it you went up to deer park with it. did you get a chance to fly it yet. I know a few years ago they complained of a rough engine and it kept the airplane from flying. glad you found the problem. what parts did they change out, very curious.

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