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hello, recently my 912 with 1100 hrs started producing lower RPMs , static during run up and climb out.

normal rpm with ( un touched prop setting ) would be 5250 run up ,5000-5200 climb out, and 5300-5450 cruise 

not sure if it’s because of the warm humid Missouri temperatures, i’m sure it plays a factor however I’m leaning towards a fuel issue as during cruise fuel pressure warning light comes on and it drops to about I think the warning light is set for 2.5 psi, to rectify I’ll put on the electric boost pump, however I don’t have to run with it in definitely once I get out to say 4500-5500 feet it’s fine and RPM seems to progressively increase, I have had the plane (TL-stingsport ). four years and I’ve never messed with the carburetors or floats and I’ve never changed the mechanical fuel pump, Air filter and plugs get changed annually ( 100 hrs per year) . I’ve never had an issue with the filter or too much oil on the filter, my last annual just about a month ago I cleaned and oiled air filter and new plugs so they’re relatively new! All else checked out ok, compressions, gearbox torque ck, however I have noticed very small particles in my fuel filter black and a very small amount of oil is coming out of my cowling hard to track down the leak it’s not very much in one it’s very minor, anyway want to check to see if anybody in the group has ever had issues with the RPM drop. Hey suspecting air fuel mixture would be my first reaction, with the humid hot air I’m thinking running rich but at the same time with the low RPM I would almost assume it’s not getting enough fuel so I’m thinking carburetor rebuild any ideas would be appreciate it safe flying and blue skies.

stingsport. 

  • Re: Lower Rpm’s

    by » 6 weeks ago


    Possibilities -

    Inspect fuel filters & carburettor float bowls for debris.

    Freshly oiled air filter(s) may be over oiled causing "strangulation" ie  reduced air flow.


  • Re: Lower Rpm’s

    by » 6 weeks ago


    I agree check the air filter a friend of mine had the same problem, reduction of rpm and realized he had over oiled the filter. I would be concerned about the particles in the filter. 

     


  • Re: Lower Rpm’s

    by » 4 weeks ago


    You stated what your normal rpm’s were.  How big was your rpm drop?  


  • Re: Lower Rpm’s

    by » 4 weeks ago


    John,

    If you are talking about circa 100 rpm difference, I think that may just be a result of summer heat and humidity. I have a 912is and just yesterday I left my home airport in the late morning when the temp was 75 degrees and I got my normal 5050 rpm on takeoff, increasing to 5100 for climb out.  Then, on the way home from the Sacramento valley in CA, it was 100 degrees on the runway and I got 4890 RPM on takeoff.  As soon as I was up in cooler air, RPM increased to 5100 RPM as I continued to climb.  I have noticed this often, and it can be alarming if you don’t anticipate it.  Where you live, in addition to heat, humidity plays a big role since the water displaces air (and O2) so you get a less dense intake charge. 

    This is a good a white paper from the FAA on density altitude.  Since most DA computations don’t consider humidity, they recommend adding 10% to your takeoff roll in known high humidity conditions.  

    https://www.faasafety.gov/files/gslac/library/documents/2011/Aug/56396/FAA%20P-8740-02%20DensityAltitude%5Bhi-res%5D%20branded.pdf

     


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