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912ULS-RPM drop down

in 912 / 914 Technical Questions 7 years ago
Hi there,
I have a new and latest model of this model installed on my powered parachute with 35HRS. I recently experience a sudden rpm dropdown during cruise at about 4000RPM at altitude of about 500ft (five hundreds). The outside temperature is between 5-12 Celsius degrees. In addition, I lately experienced rpm dropdown when accelerating the engine from 4000 to 5000. I visually inspected the carbs, tubes and the gas system for dirt but found nothing.
I have three other colleagues experiences the same problem.
Can anyone help me understanding this and what else I need to check trying to solve this problem? Is this might be related to an operation in a cold weather? I have no heating system to the carbs and I left carb's needle in the factory setup.
Thanks in advance

  • Re: 912ULS-RPM drop down

    by » 7 years ago

    You could be experiencing carburetor ice.

    Have you checked the icing chart and looked at the due point / temperature to see if you are in icing environment?
    nyc02fa025_1.jpg (You do not have access to download this file.)
      
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  • Re: 912ULS-RPM drop down

    by » 7 years ago

    Thank you for your prompt reply. This definitely can be due to icing environment. Your chart clarifies this. Are there any cold weather configuration I should consider but to install an Intake air pre-heating system? Changing the setup of the carb's needle may help? Different fuel mixture? Just thinking that my fuel tank made of metal but I have water separators installed (Is this an issue? The OM mentions to ensure "Fuel lines routing inclined". Since my fuel tank located lower than the engine, I am not sure how it will serve.
      
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  • Re: 912ULS-RPM drop down

    by » 7 years ago

    Hi,
    About this topic, I still experience the situation of RPM dropdown and disordered mostly when accelerating from 4000-->5000RPM. It takes a while for the engine to respond and it looks like kind of a choke for him.

    I am not sure the symptom solely related to icing affect. And I wish to check if there is a situation where various carburetor configurations / setup are possible and my carburetor/engine configuration doesn't fit my region where I fly (needle sizes / adjustments, etc). As my engine shipped from an authorized var, I am not sure from where it initially arrived and how it was configured. Is this possible to get this information by the engine S/N?

    I have new 912 ULS uses for powered paragliding. I remember that we used to adjust the carburetors' needle at winter time on my former 582 engine. Maybe something should be done in this direction?

    Appreciate any thought on this.
    Thank you
      
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  • Re: 912ULS-RPM drop down

    by » 7 years ago

    Hi Moshe,
    Sorry for all the extra questions, but it may help you solve your problem or lead us down the right path.

    A little more info may help us. What's the engine on, what type of air intake, have you synced the carbs, have you checked the throttle cables on the ground to make sure they are opening and closing together and smoothly without a hitch, Where are you flying (altitudes and outside temps), have you checked the carb float bowls for debris?????

    An engine rpm change could be from several factors. Most are easy to check. Does this rpm change happen all the time, is it momentary or drop and stay t at the lower rpm, does anything seem to make it change, does it happen only at take off or is it repeatable in level flight???

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

      
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  • Re: 912ULS-RPM drop down

    by » 7 years ago

    Hello Roger and thank you for your prompt reply.

    -What's the engine on: see attached
    -what type of air intake: see attached. The engine installed on the back of the aircraft and the air filter is connected directly to the carb intake (each of).
    -have you synced the carbs: The carbs are synced (as far as my knowledge goes). a certified mechanic installed and tuned the engine). This guy is helpless and don't know what else can be checked.
    -throttle cables: runs together clean and smooth. checked
    -Where are you flying: In Israel. The average flying altitude is between 0-2000ft above the sea level. The outside temps are 35- 57 F
    - have you checked the carb float bowls for debris: was visually inspected but don't remember if they are the improved once.
    -The RPM or engine coughing occurs during flight mostly when I accelerate from 3800RPM (level flight) to higher RPM speed. Than the engine gets choked for a moment and then slowly recovered.
    In a very rare frequency it happens in a level flight +/-4,000rpm without changing the throttle (it appears and disappears). It starts coughing and then recover, matter of 1-2 seconds.

    Capture2.JPG (You do not have access to download this file.)
    Capture1.JPG (You do not have access to download this file.)
    2017-08-28-PHOTO-00000523.jpg (You do not have access to download this file.)
      
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