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LOSS OF POWER/RPM

in 912 / 914 Technical Questions 9 years ago
Today I discovered that I have a loss of power and also I could not reach the usual max rpm: loss of ca 400 rpm.
When I turn over the prop I hear a soft hissing sound near the spark plugs/cylinder head on the left side.
Idle: OK.
Magneto check: OK
Electrical: seems OK
I have checked 20 Nm spark torque: OK
Carbs synch: OK
Fuel system: seems OK

Unable to find the cause yet. Any ideas?

Jan

  • Re: LOSS OF POWER/RPM

    by » 9 years ago

    You need to investigate the leak near the spark plug/cylinder head. did the coolant temps get overheated and warp the heads?
      
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  • Re: LOSS OF POWER/RPM

    by » 9 years ago

    Rob,
    Thanks for the reply.
    I have checked the engine when is was cold: a clear hissing sound appeared and lack of compression when turning the prop for the 4th time over. The hissing sound more or less disappears when the engine is warm. It could be that when it is cold toil is lacking inside the cylinder(s) giving a short loss of compression. Or is one valve or more not closing off properly?
    Anyway, I will check the compressions soon.
    Carb filters are clean.
    Spark plugs have nice colors..............
      
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  • Re: LOSS OF POWER/RPM

    by » 9 years ago

    try spraying soapy water in the area to see if you can find the hiss. It may be a spark plug or the cylinder/head surfaces?
      
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  • Re: LOSS OF POWER/RPM

    by » 9 years ago

    I had this exact problem... Seemed like it was a little underpowered on takeoff one day.... I thought my prop pitch was off... It was hot, I was at gross, max fuel etc... Was climbing like a pig....
    I think I found the problem...
    image.jpg (You do not have access to download this file.)
      
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  • Re: LOSS OF POWER/RPM

    by » 9 years ago

    Hi all,

    Just measured the compressions: all cylinders OK.......... :sick:

    The exhaust pipe of one cylinder is relatively black. Have to check the colors spark plugs of this cylinder but I guess they are back as well.

    I have checked all tolerances between the tappets and valve heads: OK.

    Still a valve problem? Ignition problem?

    Thanks.

    Jan
      
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