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rotax 447 engine failure

in 2 Stroke Technical Questions 13 years ago
on the way home from picking the new super cat I encounted engine failure.whilst cruising for around 20 mins the engine started running rough then died. I made a restart, and as the engine still run rough I gave it full thottle and it ran fine again,when dropped back to cruise after a few minites it ran rough again ,full throttle applied and ran fine,so flew home at full revs (10 mins) and dropped revs for approch and ran fine landed no issues,but when broght the revs back up for taxing ran rough again. NOTE:noticed full leaking from air filter right before start up and when taking off noticed a slight miss , checked the float level,needle and seat,fuel tap removed inspected,plugs checked (brown) air filter cleaned and oiled NOTE" float level sits about 4mil below bowl top., ran up the engine and runs fine when applying revs up slowly but always runs rough when pulling back the throttle ,push the throttle forward fast and cough and slutters.? thinking I may need to overhaul the carby (jets)? any ideas????????????? should mention was told after,that its happened before! and noticed it come with a spare(old)carbie.?

  • Re: rotax 447 engine failure

    by » 13 years ago

    Update, suspect its the electric fuel pump ,over pressure! as the fuel tank is mounted high (up front under dash like an ag hopper) and gravity feeds to carby,plus has the mechanical fuel pump, we believe the electric pump (always left on) is over pressuring the float needle and seat. will run another test tomorrow with NO electric fuel pump turned on,keep you posted
    (no pressure reg fitted.
      
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  • Re: rotax 447 engine failure

    by » 13 years ago

    Sounds like you are right. Overpressure could raise the fuel level in the bowl. When you carefully remove the bowl and remove the floats, the fuel level should be about 12mm below the top of the bowl. Turn the carb upside down and measure the distance from the float arm down to the bowl gasket. It should be about 10.5 mm and both float arms parallel with each other. Pull the float arm and drop the float valve out and check the viton tip for wear or damage.also look for trash in the float valve seat. You could have a bad float. Check to see that they are both floating at the same height. You can shake them to see if one has fuel inside. (just reread your post, sounds like you've already done all this).

    You might check the enrichener circuit. If it is not closing completely you can be running too rich.

    Everyone does it differently but I never use my electric pump except to prime the system before starting and my fuel tank is below the engine.

    Bill.
      
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  • Re: rotax 447 engine failure

    by » 13 years ago

    Could the float needle valve also be at fault...letting fuel pass when it in the cut off postion.

    Nick.
      
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  • Re: rotax 447 engine failure

    by » 13 years ago

    Nope not fuel pump!ran the same with no electric fuel pump, ran engine70% then switched off in that position and removed plugs,both ceramic,s light brown but 1 plug electrode black,will buy 2 plugs and see if not will pull down carbie and inspect and clean jets
      
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  • Re: rotax 447 engine failure

    by » 13 years ago

    Tim,

    How were the EGTs in the midrange. If they were low you might try moving the jet needle clip one notch higher to lean out the mixture.

    Bill.
      
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