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rparigor(at)suffolk.lib.n
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 Posted: Thu Dec 11, 2008 9:50 am Post subject: re - Rough 912 UL Engine Operation when Pneumatically |
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Hi Roger
"I lean out or throttle back the richest carb to equal the leaner carb.
The one with the lower vacuum is using more fuel /richer and the one with
the highest vaccum is less throttle or leaner"
When you say you are going to lean out the richest carb or throttle back,
is that one thing to do or two things you can do?
If you meant only one thing, that would be closing butterfly a bit.
If you meant two things, it would be:
closing the butterfly a bit
or
perhaps unscrewing the mixture screw a bit to allow more air (or??)?
Thx.
Ron Parigoris
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Thu Dec 11, 2008 3:03 pm Post subject: Re: re - Rough 912 UL Engine Operation when Pneumatica |
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Sorry for the misunderstanding. I was just trying to be more clear and I guess I muddied up the water. Forget I used the word lean out as that usually pertains to adjusting the jets or needles. The idle mixture screw on the bottom of the 912 carb should be set to 1.5 turns out.
Just move the carb throttle lever or bowden cable so it gets less fuel. The vacuum guage with the lower vacuum number is getting more fuel (pulling less vacuum). The vacuum guage with the higher vacuum number is getting less fuel (pulling a higher vacuum). I usually move the richer carb's bowden cable so it is getting less fuel and the vacuum guage needle moves to a higher vacuum number to equal the other carb guage. You can see which one carb to adjust or which way to move the carb throttle lever by just moving it slightly with your hand and watching the vacuum guage needle move. If it moves the wrong way then move it the other way.
Note*
Just make sure your cockpit throttle lever bottoms out to idle at the same time as the carb idle stop screw bottoms out. If the carb idle stop screw bottoms out before your throttle lever in the cockpit is all the way back then you may bend the carb throttle stop by putting too much pressure on it.
Once you have done one or two carb syncs it will be a piece of cake.
If this didn't clear it up let me know.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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rparigor(at)suffolk.lib.n
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| Posted: Fri Dec 12, 2008 11:15 am Post subject: re - Rough 912 UL Engine Operation when Pneumatically |
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Hi Roger
Curiosity question, do you ever richen or lean the pilot air screws?
What input and parameters do you use for adjustment?
I have not yet run my 914 but hear that at lower RPMs on ground because of
the different length of intake manifold tracks, the front cylinders tend
to become blackened a bit due to fuel droplets forming thus running a bit
rich. At low percentages of power running a bit leaner may help out if it
does not cause much in the way of hesitation. By unscrewing pilot air
screw it will allow more air in thus cause mixture to become leaner.
Perhaps one would start what factory recommends, unscrewing lets say 1/8
turn at a time until hesitation when advancing throttle begins, then
richen a little by screwing in pilot air screws to point where hesitation
stops?
I will be modifying the intake track of our Europa XS powered by a 914 by
adding an intercooler that is at best a convoluted mess of plumbing. There
are planes flying with this arrangement, but I suspect that mixture could
be influenced at low speeds where turbo is not working too hard?
Have made several motorcycles much happier driving around at very low
throttle settings with above listed approach.
Thx.
Ron Parigoris
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Fri Dec 12, 2008 7:54 pm Post subject: Re: re - Rough 912 UL Engine Operation when Pneumatica |
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Hi Ron,
You are correct in your deductions. I usually start with the factory idle mixture screw (i.e. 912ULS) set at 1.5 turns as per factory. At idle some engines do seem to cause a dry black soot on the plugs, but that goes away when you fly and no longer at idle. You can tweak the screws some to lean the idle mixture out some. You are also right about the intake air tubes. A 1/8 turn at a time will work just fine. Just fly/taxi each setting a time or two to make sure you get good consistent idle time on the plugs when you look at them. I had some black sooty plugs on my 912ULS on cylinders 2&4, but after I rebuilt the carbs it went away.
| | - The Matronics RotaxEngines-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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