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582 Decrease in RPM after take off

in 2 Stroke Technical Questions 4 years ago

I have a blue top 582 with an issue that I have been struggling with for some time now. Static RPM is 6200. After about a minute of running, the engine loses up to 1000 RPM and stops climbing, much to the dismay of the pilot. I have thrown the book at this problem. The engine has 25 hours TT and is fitted to a Dragonfly 582. The RPM loss is not sudden and takes about 30 second to drop off, even with the levers pushed full forward.

I have done the following:

  • Checked compression, all fine
  • Changed plugs and coils
  • Changed fuel pump and line, even bypassing the airframe fuel system and ran an electric pump straight to the carbs for troubleshooting.
  • Checked fuel tank venting, all good
  • Changed fuel filter
  • Changed propeller, repitched and adjusted as required
  • Changed "C" gearbox from 4:1 to 3:1 and changed propeller to match
  • Checked oil system for sufficient lubrication
  • Rebuilt both carbs IAW the latest manual
  • Checked throttle rigging from throttle to carbs, cables are not stretching
  • Cleaned air filters and even ran without to test
  • Checked carb sockets for leaks
  • Blanked off primer pump to eliminate possible leaks
  • Checked exhaust manifold for leaks
  • Checked muffler for blockage.

I am an experienced A&P Mechanic with years of experience mainly Lycoming, Continental, and Rotax 4 strokes, but I have never had to struggle to find a problem like I have with this little engine and quite frankly feeling a bit silly having a smoker stump me, when I am quite good with the big Contis and Lycomings.

Please help me

  • Re: 582 Decrease in RPM after take off

    by » 4 years ago

    The first thing I would suggest is to remove the exhaust manifold and inspect the piston/cylinders. 

      
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  • Re: 582 Decrease in RPM after take off

    by » 4 years ago

    It sound like a marginal fuel starvation issue.

    The carbs are not refilling as fast as need be and slowly run out of gas.

    The engine slows to match the available fuel and runs at the lower speed.

    If he were to reduce the throttle to a cruise setting for 30 seconds, the climb should return at least for 10 seconds or more.

    You might have some crud in the carb fuel fitting or passage just before the Float Valve.

     

     

     

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
    Report

  • Re: 582 Decrease in RPM after take off

    by » 4 years ago

    If a two stroke suffers restricted fuel supply while under full power it will most likely show some damage. I wouldn't suggest flying it until it has been inspected. If the plane is equipped with EGT guages there should have been a spike in the temps. 

      
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  • Re: 582 Decrease in RPM after take off

    by » 4 years ago

    Dennis Richardson wrote:

    The first thing I would suggest is to remove the exhaust manifold and inspect the piston/cylinders. 

    Hi Dennis

    Thank you for the reply

    I did this when I removed the manifold and checked the muffler, they look good

      
    Report

  • Re: 582 Decrease in RPM after take off

    by » 4 years ago

    Bill Hertzel wrote:

    It sound like a marginal fuel starvation issue.

    The carbs are not refilling as fast as need be and slowly run out of gas.

    The engine slows to match the available fuel and runs at the lower speed.

    If he were to reduce the throttle to a cruise setting for 30 seconds, the climb should return at least for 10 seconds or more.

    You might have some crud in the carb fuel fitting or passage just before the Float Valve.

     

     

     

    Hi Bill

    I ran an electrical pump to the carbs to ensure proper flow of fuel. I then removed the carb bowls and check to see how much fuel comes through the valves, and the flow is good. I went so far as to rebuild the carbs and I put new valves in. 

    Everything points to a fuel starvation issue, and like you said, retard to cruise and then reapply throttle, the RPM returns a little for a few seconds then dies again. Fuel starvation was the most obvious thing so I took a look at that first and threw every idea at this, and I have had no luck.

    Strange thing, if I overpitch the propeller so that max RPM on the ground is below 6000, say 5800 to 5500 at full throttle, the RPM stays constant.

      
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