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Thread: When to choke a 912ULS

  1. #1

    Join Date
    Sep 2012
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    Default When to choke a 912ULS

    Just curious, when do you use the choke to start your 912ULS? The manual says:

    "If engine in operating temperature, then start the engine without choke" (operator manual page 3-7)

    I live in the desert where its often 90-110F on a "cold start". I was using the choke as instructed since the temperature was not up to the operating range but I was finding the starting was not as smooth and easy as it should be in a rotax. It even flooded once rather than starting. I then stopped using the choke on a cold start when the air temp is above 90F and its started smoothly every time since. Has anyone else noticed this? At what air temperature do you stop using your choke for a cold start?

  2. #2

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    Default Re: When to choke a 912ULS

    The "choke" on a 912 equipped with Bings is not anything like the carb chokes of old, there is no butterfly to close. Instead of pulling the knob clear out try using 1/4-1/2 or less of the open position on warmer days.






    Quote Originally Posted by 3kdscf View Post
    Just curious, when do you use the choke to start your 912ULS? The manual says:

    "If engine in operating temperature, then start the engine without choke" (operator manual page 3-7)

    I live in the desert where its often 90-110F on a "cold start". I was using the choke as instructed since the temperature was not up to the operating range but I was finding the starting was not as smooth and easy as it should be in a rotax. It even flooded once rather than starting. I then stopped using the choke on a cold start when the air temp is above 90F and its started smoothly every time since. Has anyone else noticed this? At what air temperature do you stop using your choke for a cold start?

  3. #3

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    Default Re: When to choke a 912ULS

    Quote Originally Posted by ScottS97385 View Post
    The "choke" on a 912 equipped with Bings is not anything like the carb chokes of old, there is no butterfly to close. Instead of pulling the knob clear out try using 1/4-1/2 or less of the open position on warmer days.
    Thanks. Was not aware that you could partially engage the choke but it makes sense with the V shape of the opening.

  4. #4
    Super Moderator Av8r3400's Avatar
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    Default Re: When to choke a 912ULS

    The "choke" is an enrichening circuit internal to the carburetors on a Bing 64.

    It is not a proportional valve. It either opens or closes a circuit allowing more fuel to pass into the throat of the carburetor when the throttle is less than 10% open.

    If you are having hard starting issues, often narrowing the gap on the spark plugs from .7mm (.0275") to .5mm (.020") can help this.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  5. #5

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    Default Re: When to choke a 912ULS

    Quote Originally Posted by Av8r3400 View Post
    The "choke" is an enrichening circuit internal to the carburetors on a Bing 64.

    It is not a proportional valve. It either opens or closes a circuit allowing more fuel to pass into the throat of the carburetor when the throttle is less than 10% open.

    If you are having hard starting issues, often narrowing the gap on the spark plugs from .7mm (.0275") to .5mm (.020") can help this.
    I beg to differ on the valve not being proportional, I slowly push the tee knob in(mine is the locking type) as the engine warms.

  6. #6

    Join Date
    Sep 2017
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    Raleigh, NC
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    Default Re: When to choke a 912ULS

    I understand what Mangy is saying. If you look at how the starting circuit works, there are tiny holes that, when the "choke" is engaged, air is re-directed through a completely different pathway with it's own air fuel mixing. It would seem that the only way air flow, knowing it likes the path of least resistance, could be directed through this alternate pathway is for the choke to be fully engaged. That being said, I too have experienced a proportionate improvement in engine smoothness as i push the choke back in. I have never intentionally moved the control slowly though. I will try that the next time i fly and see what happens.
    Brian Cass
    KF Model IV Speedster
    Rotax 912UL

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