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     Today I was flying to a fly in at Natchez Mississippi. Flying my Aircam. I was flying at 5000 RPMs. After one and a half hours of flying, the right engine began to lose power. The RPMs drop down to around 3500. There was an ag strip below me so I landed. Did the mag check. everything OK. Other than let the engine sit for 10 minutes, I didn't do anything else. Upon restart, the engine would maintain 4000 RPMs. But no more. I took off with both engines at 4000 RPMs and flew to the next airport. After the plane sat for approximately three hours, I attempted to run the right engine again. It would not go over 3500 RPMs. There was a mechanic on the  field. He removed the bottom spark plugs on three of the cylinders just to see what they look like. They were clean. I Then crank the engine. At that point I had full throttle up to 5200 RPMs. I took off and flew for two hours at 5000 RPMs on both engines with no further problems.

    The same thing happened 2 weeks ago on a local flight but alter landing it cleared up.  I had full throttle.     
    The only other thing going on with the engine is about a month ago, my coolant level was down a half inch. In four years of flying, I have never had to add any coolant. The plastic overflow bottle was still half full. The reservoir on top of the engine was a little low.

     After the mishap today, I noticed that the plastic overflow bottle was almost full. The reservoir on top was a little low.

  When the problem shows up, I can advance the throttle smoothly to 3500 or 4000 RPMs. After that, it starts getting mushy are bogging down.   

Any ideas on what to look at?

     

  • Re: Engine losing power

    by » one month ago


    Check the fuel tank vents. 

     

    Alan


    Thank you said by: Keith Wall

  • Re: Engine losing power

    by » one month ago


    As Alan points out double check the vents, but my money is on carb bowl debris. Pop the carb bowls off and check them to rule this in or out. The symptoms sound more like debris to me. While two bowls are off on each engine one at a time you can place a catch basin under each bowl on that engine and flip the electric pump on for a few seconds to flush anything that might be in the carb hose or carb. Do most common and inexpensive diagnostics first before jumping to less common causes.

     

    p.s.

    Any maintenance just before this happened?


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


  • Re: Engine losing power

    by » one month ago


    After the 1st instance, I used my carbmate to synchronize the carbs.  
    no other maintenance done.

    thanks for the tip.


  • Re: Engine losing power

    by » 6 weeks ago


    I had similar behavior on a 912ULS and we went after every component in the fuel system from the tank to the bowl and behavior was the same for us - - loss of RPM in cruise.  Appeared to improve after cool down / tax back and then on climb or at cruise, it was as though someone was reducing the throttle.  Running smooth, just idle lowering.  We checked the cables and linkages etc.   Run up to 4K RPM was always fine.  Brief periods over 5K seemed OK but then RPM started dropping down to around 4K.

    Finally swapped the mags and problem solved.  Apparently one mag could run great up to 4K RPM, then once warm, couldn't get over that.  Other was weak.    

    Hope this is useful - let me know.

    Dave


  • Re: Engine losing power

    by » 6 weeks ago


    Thanks for the tip.  I was flying today and thought about the mags.  Lately my B mag is intermittent.  Mag check prior to takeoff  will be good and then when I land, the B mag won't work. Engine keeps running and I have to use the prime to kill the engine.  I check the two wires going to the mags and then they work correctly. Intermittent problem.  
    not sure how that would cause the engine to lose power at cruise.


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