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1. 10:13 AM - Carbs - enrichener - cold start. (B)
2. 10:58 AM - Re: Carbs - enrichener - cold start. (Stuart Harner)
Message 1
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| Subject: | Carbs - enrichener - cold start. |
"However, I don't quite understand when you said the enricher does not
work unless the throttle is closed."
Maybe I should have been more clear...
When starting a Cold engine, and the starter is turning 300 rpm or there
about,,, very little air is going through the carb. Compaired to an
engine idleing at 1800 rpm or running at 5000 rpm in cruise.
With the small amount of air going through the carb while being cranked and
the main throat of the carb open.... Only a fraction of the air will go
through the enrichener circuit at a rather slow rate of speed. If it can't
create enough vacuum on the fuel suction port to lift the fuel you don't
get fuel or the full benefit. And if you get some fuel through the
enrichener, but most of the air is bypassing the enrichener the mixed air
is not as rich as it could be.
On a cold engine, if only half the fuel is vaporising, the air fuel air
mix exposed to the spark plug will not fire.
If you close the main carburetor and force all the air through the
enrichenor, it will pull all the fuel in the enrichener reservoir very
quickly, if half is vaporized, the hope is that the fuel air mix at the
spark plug will be in the range where it will burn.
When the engine is hot,,, hopefully all of the fuel will vaporize. At
that point the engine will start running rough. That is the time to close
the enrichener and run on the main jet, and or the needle jet and needle.
If your engine is constantly running too hot you can open the enrichenor
richen up the mixture and cool the engine down. If that happens you
should rejet the engine.
If the engine does not start right away, let the starter rest for several
seconds to allow the enrichenor reservoir in the float bowl to refill.
Quoting from the operator's manual for all versions of rotax 912 page 10
- 19
quote
cold start:
with throttle closed and choke activated (open throttle renders the
starting carb ineffective.) close quote
If it makes more sense substitute the word enrichenor for the word "choke"
and also the words "starting carb"
Boyd Young
Mkiii 988 hours
Northern Utah
Message 2
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| Subject: | Re: Carbs - enrichener - cold start. |
Interesting. I did not know they used the 54 on the 912 engine.
In my case it is a 447 with a recoil starter. It starts easily and runs
quite well as set up from the factory with the exception that I had to
lower the needle clip (raise the needle) one notch. Most of my flying is
done at 2000 to 3000 MSL. As long as the prop is loaded everything works
as expected but if I should un-load the prop for more than about 30
seconds it will cause the EGT's to climb into the red zone. I don't
remember the exact temp that I have set the alarm for but it is below
what Rotax says should be the max.
This is usually not a problem at the upper end of the throttle but can
be when reducing power for descent and nose down unloads the prop and
there you go. This is usually in an RPM band around 4000. It seemed to
me that this is caused by the engine running lean and the enricher lever
was the closest thing to mixture I had available. Opening the enricher
adds just enough fuel so that the EGT stays within specs and seems to
work fine.
The only time I had a problem with it was after landing I forgot to
close the enricher and as soon as I closed the throttle all the way, the
engine quit. Enricher off, throttle closed and a quick pull of the rope
had me going again.
Not knowing the details of the design and just looking at it, it appears
that the enricher sucks up fuel from the small chamber in the bowl
through the dip tube and dumps it into the throat of the carb. My guess
was that the vaporization was taking place in the intake and crankcase
as the fuel and air mixed and tumbled around.
I haven't had the carb apart in years, so the next time I open it up I
will be studying it more thoroughly.
Thanks for all the info.
Stuart
On 1/21/23 12:13, B wrote:
> "However, I don't quite understand when you said the enricher does not
> work unless the throttle is closed."
>
> Maybe I should have been more clear...
> When starting a Cold engine, and the starter is turning 300 rpm or
> there about,,, very little air is going through the carb. Compaired
> to an engine idleing at 1800 rpm or running at 5000 rpm in cruise.
> With the small amount of air going through the carb while being
> cranked and the main throat of the carb open.... Only a fraction of
> the air will go through the enrichener circuit at a rather slow rate
> of speed. If it can't create enough vacuum on the fuel suction port
> to lift the fuel you don't get fuel or the full benefit. And if you
> get some fuel through the enrichener, but most of the air is bypassing
> the enrichener the mixed air is not as rich as it could be.
>
> On a cold engine, if only half the fuel is vaporising, the air fuel
> air mix exposed to the spark plug will not fire.
>
> If you close the main carburetor and force all the air through the
> enrichenor, it will pull all the fuel in the enrichener reservoir
> very quickly, if half is vaporized, the hope is that the fuel air mix
> at the spark plug will be in the range where it will burn.
>
> When the engine is hot,,, hopefully all of the fuel will vaporize.
> At that point the engine will start running rough. That is the time
> to close the enrichener and run on the main jet, and or the needle jet
> and needle.
>
> If your engine is constantly running too hot you can open the
> enrichenor richen up the mixture and cool the engine down. If that
> happens you should rejet the engine.
>
> If the engine does not start right away, let the starter rest for
> several seconds to allow the enrichenor reservoir in the float bowl to
> refill.
>
> Quoting from the operator's manual for all versions of rotax 912
> page 10 - 19
> quote
> cold start:
> with throttle closed and choke activated (open throttle renders the
> starting carb ineffective.) close quote
>
> If it makes more sense substitute the word enrichenor for the word
> "choke" and also the words "starting carb"
>
> Boyd Young
> Mkiii 988 hours
> Northern Utah
>
>
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