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choke throws carb sync off

in 912 / 914 Technical Questions 13 years ago
The carbs on my 912uls are well balanced, very smooth, but when i start the engine cold with the choke it seems to throw the sync off moderately. I checked for cable stretching and the carb cables seem to hit the stops together, so what else might be causing this???
thanks,
Key

  • Re: choke throws carb sync off

    by » 13 years ago

    Hi Key,
    A little more info will help.

    Once warm does it idle smooth at 1700-1800 rpm?
    At first start and in cool weather it may be slightly rougher than warm and at first start idle should be around 2200-2400.
    Either the chokes aren't opening equally and all the way or like the person the other day here, you have a clog in the idle or choke circuit.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: choke throws carb sync off

    by » 13 years ago

    Thanks Roger

    Yes, the engine idles very smoothly at around 1750 as soon as i push the choke in. I do warm it up around 2300rpm and it smooths out a bit as i start to ease in the choke and give it a tad of throttle. As far as i can tell the chokes hit their stops together (though it is hard to be precise), so perhaps i do have some clogging in one of the choke circuits. The imbalance when choked is not terrible, i just worry about the gearbox when i start it.

    Key
      
    Report

  • Re: choke throws carb sync off

    by » 13 years ago

    Hi Key,

    It sounds like what your telling me is a normal start up. Most 912ULS engines are rougher with the choke on than off. If it only runs a little rough with the choke on and it is synced and smooth with the choke off and warm then you may be worrying about nothing. It sounds like your okay. You shouldn't worry about the sync when the chokes are on. It isn't something you should be doing.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: choke throws carb sync off

    by » 13 years ago

    Hi Key,

    It sounds like what your telling me is a normal start up. Most 912ULS engines are rougher with the choke on than off. If it only runs a little rough with the choke on and it is synced and smooth with the choke off and warm then you may be worrying about nothing. It sounds like your okay. You shouldn't worry about the sync when the chokes are on. It isn't something you should be doing.


    The poor Bing 64 is much maligned and misunderstood. In this case, the Bing 64's "choke" looks like a choke, acts like a choke but isn't a choke.

    In fact, the Bing 64 carb installed on Rotax 912-series engines does not have a choke. There is no choke. The Bing 64 has a rotary valve starting carburetor. Yes, two carburetors in one, with the rotary valve starting carburetor having the sole purpose of starting the engine (surprise). This is why it's required by Rotax that the throttle be completely closed when starting the engine, so that the throttle plate (throttle valve) is completely closed and sufficient vacuum is available to the starting carb.
    BingType64.pdf (You do not have access to download this file.)
    Thank you said by:
      
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