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Thread: 912ULS Engine stumbled in flight

  1. #11
    Senior Member Slyfox's Avatar
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    Dec 2008
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    felts field, spokane
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    1,285

    Default Re: 912ULS Engine stumbled in flight

    I just looked at your pics and your setup looks just like mine. meaning the left carb and intake was put on the right side and vice versa on the other carb. so your right carb will have the issue with the float bowl. hope this helps
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  2. #12
    Birdseyeview's Avatar
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    Sep 2017
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    Oregon, Ill
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    181

    Default Re: 912ULS Engine stumbled in flight

    Thanks for all the input. I replaced the see through plastic paper element fuel filters, took the high spot out of the fuel-in line to the fuel pump and realigned a float valve armature that was slightly misaligned. I also discovered that the same carb had rotated inboard about 8 degrees. I re-leveled the carb and a subsequent test flight proved the engine was running fine (no missing). So far so good after an hour run time.
    Larry Olson
    Kitfox Series 6 - 1st Flight Oct 2021
    Tri-gear, smooth cowl
    912 ULS

  3. #13
    Birdseyeview's Avatar
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    Default Re: 912ULS Engine stumbled in flight

    On a subsequent recheck of the carbs to see if they had rotated inboard again I discovered that the left carb had backed out of its rubber socket about 1/4". I had previously installed a short metal tube spacer on the screw that tightens the carb hold down clamp to prevent over tightening. Apparently it didn't tighten the carb clamp down enough to prevent it from walking out of its rubber socket. I highly suspect this was the culprit to my rough running all along. I removed the spacers and tightened both clamps down. Also, when I replaced the temporary plastic see through fuel filter I blew through it so I could compare its resistance to that of the original metal filter that Kitfox supplied. The metal filter was dramatically more free flowing (less resistance) that the plastic see through filter. Another reason not to use the see through plastic fuel filters. On a subsequent flight the engine ran smooth as silk. Lesson learned for me is to add a step to my condition inspection to see if carbs have backed out or rotated in their rubber sockets. I hope others benefit from my findings.
    Larry Olson
    Kitfox Series 6 - 1st Flight Oct 2021
    Tri-gear, smooth cowl
    912 ULS

  4. #14

    Join Date
    Dec 2009
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    Lawrenceville, GA
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    169

    Default Re: 912ULS Engine stumbled in flight

    Quote Originally Posted by Slyfox View Post
    Do you have any thing that says whether or not these are resistant to alcohol?
    Building a KF IV Classic

  5. #15
    Senior Member Dave S's Avatar
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    Oct 2008
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    St Paul, MN
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    Default Re: 912ULS Engine stumbled in flight

    Hi Larry,

    One thing I didn't pick up on right away from your photos had to do with a change Rotax made to help with keeping the carbs in place on the sockets. Please see my attached photo - top front of the carb diaphragm chamber. At one point Rotax added a clamp to the manifold crossover tube on each side to connect a spring to the top front screw of the carb diaphragm chamber. I don't see this on our original photo so suspect the engine was made before this change occurred. I believe the purpose of this additional securement was to remove some of the downward/backward pressure on the carb socket. I can't tell from the photo if your application has any securements other than clamp going around the carb socket.
    Attached Images Attached Images
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

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