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After normal mx, our 912uls (approx 700 hrs) is running extremely rough.  So rough that a carb sync is not possible.  Local AP IA is assisting, not a rotax guru, but is familiar with them.  He thinks a carb is not functioning.  

 

Here is a summary - Installed on a Vans RV-12

 

-Gearbox overhaul by Lockwood - all ok and re-installed on a/c

-Both carbs had the "5 year" overhaul by Lockwood

-New air filters

-New spark plugs, gapped properly (.28)

-Replaced a carb drip tray

-New engine mount isolators

-Throttle cables reinstalled on carbs per VANS Kit Assembly Instructions (never removed from carb mounting bracket)

-Did not change oil, so no need for oil purge

-Floats weighed within spec (each around 6g per set)

-Ignition check on last ground run was well within specs (prior to condition inspection)

 

Engine was running fine when last run (about a month ago before the condition inspection)

 

Pulled plugs and all look to have been firing

 

Engine starts OK - and "soft start" seems to be working, roughness from the start.  

 

Fuel is getting to both carbs equally

 

As rough as it was running, no fuel overflowed into the overflow tubes or drip trays

 

More troubleshooting to commence - 

  • Re: Rough running 912ULS after mx

    by » 11 months ago


    If you stop the engine when it is running rough and carefully remove the float bowls, are the fuel levels even and the correct distance down from the top edge?

    Is there any debris in the float chamber?

    Are there any blockages in the fine drillings just in front of the butterfly valve?

    Has the choke mechanism been installed correctly?


  • Re: Rough running 912ULS after mx

    by » 11 months ago


    Fuel bowl levels are equal

    No debris detected.....

    choke mechanism seems to be working properly, used to start engine initially...


  • Re: Rough running 912ULS after mx

    by » 11 months ago


    Air leak somewhere? Test by spraying some carb cleaner around the carbs if you can shelter it from prop wash.

    O ring missed off one of the mixture screws?

    Needle in correct position?

    Sliders free to move?

    Split carb mounting rubber?


  • Re: Rough running 912ULS after mx

    by » 11 months ago


    I am with Kevin on - Split carb mounting rubber?

     


  • Re: Rough running 912ULS after mx

    by » 11 months ago


    Kevin Stewart wrote:

    Air leak somewhere? Test by spraying some carb cleaner around the carbs if you can shelter it from prop wash.

    O ring missed off one of the mixture screws?

    Needle in correct position?

    Sliders free to move?

    Split carb mounting rubber?

    Carbs were "overhauled" by Lockwood, assuming that all o-rings went back in, but you know how that goes.  AP verified needle position, sliders work ok.

     

    Mounting rubber was replaced last year and o ring in place on manifold. 


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