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This poor Kitfox with a 914UL was crashed on takeoff and turned over on its back.  The pilot got some pretty bad bumps, but the airplane got the worst of it.  The engine was removed from the bent fuselage (wings received very little damage) and fit on a factory-fresh airframe and given a 5-yr rubber replacement.  The engine starts easily and quickly, runs smoothly at idle.    But when the throttle is advanced the engine stumbles and stalls. Fuel pressure either on both pumps or one or the other is within specs. The TLR logs show nothing unusual.  The engine starts up right away again with no hesitation or complaints.  It acts as if the carbs are not keeping up with the demand for higher RPM.  Has anyone else had this stalling problem on a 914 after an engine change/rubber replacement?   I'm stumped because she starts right up and idles so easily.    

7798_1_Ouch.jpg (You do not have access to download this file.)
  • Re: 914 stalls above idle

    by » one month ago


    Did the aircraft crash because the engine failed or some other reason?

    When the throttle is advanced, does the Stumble and Stall happen concurrent with the power change or does the engine initially power up and then fail a number of seconds later?

     

     


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    whertzel1@yahoo.com
    Clicking the "Thank You" is appreciated by all.

    Thank you said by: Jeffrey Fritts

  • Re: 914 stalls above idle

    by » one month ago


    Thank you, Bill, for helping me out. 

    No, N702KF didn't have and engine failure on takeoff.  This accident happened at a bush strip at Owyhee Reservoir in eastern Oregon.  The low tailwheel time pilot got to close to the edge of a narrow runway and caught a wheel and took an excursion off the side.  

    The latter.  When we moved the engine from the damaged fuselage to the new one the wastegate cable to the servo motor had to be removed and refit.  The cable was reinstalled and the throttle position sensor was calibrated.  According to the TCU log when the throttle is advanced from throttle position 0 to 8.3 the RPMs increase to 3300 then quickly falls off and the engine stalls if the throttle is not returned to idle.  This takes 8 seconds once again according to the TCU log that we downloaded. 

    So I guess the uncomplicated answer is you shove the throttle in the engine speeds up like you would expect it too and then RPMs start dropping off.  She seems to have no trouble increasing RPMs but will not stay there.  

    25118_2_TCU Log 002.xls (You do not have access to download this file.)

  • Re: 914 stalls above idle

    by » one month ago


    Well, that sounds like it is sucking the Float bowls dry faster than they can be re-filled.

    I would look at a fuel starvation issue.

    There is enough fuel flow for idle and slightly above, but not enough for the higher power settings.

    Debris in the Filters and/or Hoses and Fittings would be the first thing to look for.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    whertzel1@yahoo.com
    Clicking the "Thank You" is appreciated by all.

    Thank you said by: Jeffrey Fritts

  • Re: 914 stalls above idle

    by » one month ago


    Have you checked your float bowls. On the 914 it is easy to over torque the bolt that holds them on, resulting in air leak that causes too lean a mixture at high power settings.


    Thank you said by: Jeffrey Fritts

  • Re: 914 stalls above idle

    by » one month ago


    Ken is on to something. I have found that as a general rule, engines that start and idle fine but stall when throttle is applied do so because of too much air and not enough fuel. 


    Thank you said by: Jeffrey Fritts

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