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912UL Engine vibration on throttle back

in 912 / 914 Technical Questions 12 years ago

  • Re: 912UL Engine vibration on throttle back

    by » 12 years ago

    Hi Arthur,

    There are several things that may affect this. The first thing to do since this is and older engine that has 980 hrs. on it is to do a carb rebuild and clean them well.What year was the engine built? If you know the prop is good for 5700+ rpm then that isn't the issue. You shouldn't be pulling plugs out and running the engine. It's a sure fire way to trash the ignition system. Make sure the plug gaps are within the correct gap specs. This can affect the mag drop if they are too close or too wide which in turns affects the smoothness. If it were my personal plane I would do the carbs first thing and get them synced good before I worried about any other items. Bouncing around for a diagnoses could take forever and be expensive.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 12 years ago

    I also had rough running of my 912uls when i pulled the throttle for decent. I found the previous owner had extenxed the static pressure tubes on the carbs to the bottom of the cowl and out into the airflow. This is a definate no no and I pulled the extentions off and put them in the bin
      
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  • Re: 912UL Engine vibration on throttle back

    by » 12 years ago

    I have now bit the rather hard bullet of installing new carburettor kits (The float needle seat is damaged by a worn float needle and that means that one has to replace the entire carburettor housing, something I wish to avoid). I didn't find any major wear on the old parts, except a broken o-ring here and there. A major problem is that my engine has two of the same choke assemblies installed, both are marked "R" on the shaft. Since I shouldn't really have to use the choke, I rotated the wrong one so it is always closed. In its normal closed position the wrong choke assembly should have given me a lean mixture on cylinders 1/3 in the past but since these are not my problem cylinders I don't think that this mattered.

    I'll still synchronize the carbs and then report back. All this would, in any case, not answer the questions of the guys who have this problem on new less than 100hrs engines.
      
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  • Re: 912UL Engine vibration on throttle back

    by » 12 years ago

    I have now bit the rather hard bullet of installing new carburettor kits (The float needle seat is damaged by a worn float needle and that means that one has to replace the entire carburettor housing, something I wish to avoid). I didn't find any major wear on the old parts, except a broken o-ring here and there. A major problem is that my engine has two of the same choke assemblies installed, both are marked "R" on the shaft. Since I shouldn't really have to use the choke, I rotated the wrong one so it is always closed. In its normal closed position the wrong choke assembly should have given me a lean mixture on cylinders 1/3 in the past but since these are not my problem cylinders I don't think that this mattered.

    I'll still synchronize the carbs and then report back. All this would, in any case, not answer the questions of the guys who have this problem on new less than 100hrs engines.


    There is no "choke" on the Bing 64 carb. The thing that is commonly described as a choke is a separate rotary valve starting carburetor that feeds a rich mixture to the engine through a completely separate starting jet. If one of your starting carbs is incorrectly assembled it's quite possible that this is the cause of your high EGTs. Is your engine hard to start? Do you have noticeable vibration?
      
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  • Re: 912UL Engine vibration on throttle back

    by » 12 years ago

    Hi Arthur,

    I would get my enrichers assembly fixed or replaced and the float needle seat fixed. Then you'll be done with it. You will most likely need the chokes at some time. I would get everything up to date and know you're on solid ground so to speak. Carbs do need to be rebuilt every so many years regardless of hours. "O" rings dry out and crack or break, float needles wear and other parts tolerances change from wear. This is the heart of the engine and without a good heart trouble may be in your future. I just did a carb rebuild for a 2001 912A the other day. All the O rings were shot, parts had old dry gas on them and the needle valve was the old red tip that hasn't been used for many years. He was having hard starting issues.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report
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