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Thread: Rough Running Rotax

  1. #1
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    Default Rough Running Rotax

    I'v got a 503 in an Osprey hull, a few weeks back I removed the engine to fit a new fan hub, replacing the blades at the same angle as I removed them. Now it will rev to 4500 rpm ok above that it starts to run rough.It used to rev to 5800 smoothly. I'v cleaned the carbs,filled with fresh fuel,checked plugs and leads and no improvement. Any ideas whats up? Philip

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    Default Re: Rough Running Rotax

    Hi



    Sorry to hear that you're stil having trouble.



    Did you try putting the old exhaust back on just to see if thats upsetting things?



    Did you try switching out each ignition in turn to see if that affects things?



    Or disconnect the kill lines completely to see if they are leaking to earth slightly?



    Fuel pump OK? (Pump on the primer bulb a few times to "assist" it, if that clears it up then could be the fuel pump not up to scratch or the pulse line blocked/kinked/perished)



    Air filter? If it's paper based, I have known them go bad after getting wet, foam based are best for the Rotax if they can get wet.



    Ignition high tension lines all clean and in good order?



    Cheers

    Ian

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    Default Re: Rough Running Rotax

    Yes

    Yes

    Yes

    Yes

    Changed filter

    Yes

    and it still wont run smoothly. What am I missing? Philip

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    Default Re: Rough Running Rotax

    Excuse the back to basics approach, might jog some idea:



    Fuel:



    Starvation:

    Strainer in tank

    Kinked pipe

    Filter blocked/clogged

    Pulse pump not working properly:

    Pulse line kinked

    Connected backwards (OK OK....!!!! had to say it)

    Dirt in carb:

    Float valve blocked

    Main jet blocked

    Float damaged or not assembled properly

    Carbs not opening properly



    Air:



    Filter blocked (K&N type bad after getting wet)

    Something getting sucked onto filter



    Ignition:



    Spark plugs

    Coils & leads clean

    Kill line leaking to earth (disconnect near ig unit)

    Advance retard not working (strobe)

    Ignition unit not good (would have to be both gone bad, unlikely)



    Other:

    Are the blades really in the same angle? Could there have been some mistake?

    Belt too tight (absorbing excess power)



    Cheers

    Ian






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    Default Re: Rough Running Rotax

    Thanks again Ian,

    The engine stars good, runs ok till approx 4-4500 Rpm, it will make 5700 but will be runnning very rough,fault is very consitant. Before I removed the engine it was running perfectly.While it was out it would have been on its end a few times.

    All fuel should be ok, I have clean lines and filters, I'v cleaned the carbs,bowls jets etc, all seem ok,I'v tried pumping with the primer bulb-no change.

    Air, clean & dry foam filters.

    Ignition, I'v disconnected kill wire-no difference, both systems working.Plugs ok. <u>ADVANCE RETARD</u>? is this a possibility? I'm not a petrol head, disel in my viens. How do I check it?

    Blades were fitted in same sequence and angle as previous owner had them set. Belt tension is also the same. Philip

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    Default Re: Rough Running Rotax

    put the old blades back on, and check the rpm again.



    have you got the same type blades? 4z/ 5z



    Mart

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    Default Re: Rough Running Rotax

    Same blades, same pitch 5z. Philip

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    Default Re: Rough Running Rotax

    try yet another set of plugs

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