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Good evening

Sunday evening problem after an afternoon where MCR4S 914 was taken in and out of the hangar between showers:


Between 3200 and 3600 rpm the engine shake a bit and when I put the power slowly the rpm are not increasing with linearity, it take 2-3 secondes for RPM to increase


Propeller variable pitch left normal (take off mode)
Symptoms when engine cold or hot whatever
Nothing abnormal between 1800-3200 and 3600-5800
Manifold pressure normally reach at 5800 rpm as 40
Test with TCU of the TURBO ON and OFF, same symptms
Synchronized Carbs (Carbmate) normal from 1800 to 5800, even in the 3200-3600rpm range
Waste gate oiled recently with WD40

Distended waste gate cable ?
Opening sensor of carburetor (for TCU) malfunction ?

Any ideas more than welcome

Thanks

Jerome
  • Re: 914 issues between 3200-3600 rpm

    by » 9 years ago


    Check for sticky carburetor piston slides up and down easily (not sticking) and that the idle jet is clean and not obstructed. Sounds like it is not transitioning from low to high speed jets for some reason maybe one of the above suggestions.

    Thank you said by: meynie jerome

  • Re: 914 issues between 3200-3600 rpm

    by » 9 years ago


    Hello Jerome,

    Let us assume that the turbo system works well and that the silent blocks the engine mount are in good shape.

    In addition, I assume that the gearbox is OK.

    Then the behavior you report could be due to some fault either in the ignition system and/or fuel system.

    Did the problem show its face suddenly or gradually?

    Re: fuel system
    I assume that the carbs are well synchronized. Are they recently overhauled? Rubber membrane intact and well placed?
    Rubber sockets OK? Air filters clean? Mag drops OK? Colour sparks plugs normal? Fuel pressure variation? Fuel pump latest model? Floaters OK? No leak between carb body and float chambers?

    Re: ignition system
    Spark plug caps fully tight? All electrical connections fully home? Coils OK?

    How many hours has the engine?

    Good luck Jan

    Thank you said by: meynie jerome

  • Re: 914 issues between 3200-3600 rpm

    by » 9 years ago


    Mes excuses.

    Forgot to bring up the following.

    Has the propellor been damaged?

    Please note that ROTAX engines exhibit harmonic vibrations around 3600 RPM. When not properly damped this could lead to significant excitations of structural parts having harmonics around the same harmonics as the engine.

    Jan.

    Thank you said by: meynie jerome

  • Re: 914 issues between 3200-3600 rpm

    by » 9 years ago


    Hi Jan


    >>Let us assume that the turbo system works well and that the silent blocks the engine mount are in good shape.

    YES


    >>In addition, I assume that the gearbox is OK.

    YES no deposit on magnetic plug when servicing oil


    >>Then the behavior you report could be due to some fault either in the ignition system and/or fuel system.
    >>Did the problem show its face suddenly or gradually?

    Having some doubt now ...


    >>Re: fuel system
    I assume that the carbs are well synchronized. Are they recently overhauled? Rubber membrane intact and well placed?
    Rubber sockets OK? Air filters clean? Mag drops OK? Colour sparks plugs normal? Fuel pressure variation? Fuel pump latest model? Floaters OK? No leak between carb body and float chambers?

    CARB SERVICE done recently
    MAG drop 3800 -> 3700 and 3600
    fuel pump old 2003 but fuel pressure constant between 3200-3600 rpm (as when trembling shaking)

    >>Re: ignition system
    Spark plug caps fully tight? All electrical connections fully home? Coils OK?

    YES

    >> How many hours has the engine?

    400h 2003


    Changed air tubes (New) between carb today and T junction to solenoid valve at airbox BUT STILL THE 3200-3600 trembling ... :(

  • Re: 914 issues between 3200-3600 rpm

    by » 9 years ago


    >>Has the propellor been damaged?

    NOPE

    >>Please note that ROTAX engines exhibit harmonic vibrations around 3600 RPM. When not properly damped this could lead to significant excitations of structural parts having harmonics around the same harmonics as the engine.

    OK will recheck the damper/engine silent bloc tomorrow

    Thanks

    Jerome

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