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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by allsure
G'day


I am now installing my Rotax 912S engine and would appreciate some advice.


Has anyone using a Rotax had any problem with carby ice?


I am using the standard carbs and airfilters (as supplied by MAM) and if carby heat is required just how should I do it?


Thanks and regards


Ian Donaldson

Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by Bob Patterson
Hi Ian !

Alarms are sounding !!! The "S" has a <special> intake manifold
AND a special exhaust system designed & supplied by ROTAX - if you
are not using that, you WILL NOT get anywhere NEAR 100 hp. !!!
If you use the Rotax manifold, you will already have warmer air,
as the aluminum will soak up some of the heat from the surrounding
air.

I've been flying the regular 912 in the Rebel for 11 years
now, and have never even been CLOSE to having carb ice ! If you have
any doubts, get an indoor/outdoor electronic thermometer (we used
Radio Shack), and put the probe in the engine compartment, right near
the air filter. This will give you cockpit air temp, and engine
intake air temp. We've never seen intake air cooler than about 15 C.,
even in winter - it's usually more like 30 C. in summer. All that
warm air means the engine is likely not producing as much power as
it might, BUT - there's NO chance of carb ice, so I can live with
THAT !!! :-)

Regulations in your area might insist on carb heat - if they
do, you can add a simple box on the muffler, but you will LIKELY
<NEVER> NEED IT !!! ( Rotax specifically advise against any additional
heat.)

You should never try to fly the 912 until the oil has reached
<at least> 120 F. - this can take as long as 20 minutes sometimes !
This is very important, as cool oil will cause an over-pressure
problem, AND steals a LOT of power, too ! If the oil is warm enough,
the air certainly will be, too !

You will LOVE the Rebel with the 912 ! I've had the GREAT
pleasure of test flying one with this setup recently, and it has
reinforced my love of the Rebel with the 912 - what a GREAT airplane !!

......bobp

------------------------------orig.---------------------------------
At 10:08 PM 9/6/01 +1000, you wrote:
G'day


I am now installing my Rotax 912S engine and would appreciate some advice.


Has anyone using a Rotax had any problem with carby ice?


I am using the standard carbs and airfilters (as supplied by MAM) and if
carby heat is required just how should I do it?

Thanks and regards


Ian Donaldson


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<DIV><FONT size=2>G'day</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT size=2>I am now installing&nbsp;my Rotax 912S engine and would
appreciate some advice.</FONT></DIV>
<DIV><FONT size=2></FONT>&nbsp;</DIV>
<DIV><FONT size=2></FONT>&nbsp;</DIV>
<DIV><FONT size=2>Has anyone using a Rotax had any problem with carby
ice?</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT size=2></FONT>&nbsp;</DIV>
<DIV><FONT size=2>I am using the standard carbs and airfilters (as supplied by
MAM)&nbsp; and if carby heat is required just how should I&nbsp;do
it?</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT size=2>Thanks and regards</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT size=2>Ian Donaldson</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV></BODY></HTML>


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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by Legeorgen
Hi Ian,

Are you using the Rotax airbox? There is a carb heat box for the Rotax 912
engines. I'm not sure if Rotax provides the heat box or if it's an after
market product. Skystar provides one if you want it.

As for carburetor icing...I have never heard of anyone experiencing carb
icing on the 912. I don't even know of anyone who has installed carburetor
heat on their 912. I don't use it myself. The location of the Bing
carburetors on top of the engine and behind the manifold may provide
sufficient heat to prevent icing. I'm not sure why but it doesn't seem to be
a problem. Rotax engine manual says to use carburetor heat but I believe it
is for Liability reasons only.

Are you using a light prop, like a Warp Drive? Make sure you tap a hole on
each side of the carburetor to attach more springs than the one spring Rotax
uses. If you don't, you will shake those carburetors right out of their
rubber boots on start up. Skystar Details this procedure in there engine
install manual for all 912S Rotax engines.

Bruce 357R



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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by Legeorgen
Bob and Ian,

The 912S without the Rotax airbox and exhaust will still develop 95 HP. This
it from Eric Tucker... i.e. Mr. Rotax himself.

Bob, your 80 HP 912 never really developed 80 HP either, but it never really
seemed to matter. They are still one of the best weight to power ratio
engines around and they get up and go, don't they?

Ian, you'll really like that 912S, and if you ever get Bob down to your end
of the world and give him a ride, he would notice a big difference from his
standard 912UL. YEA HA!

Blue skies and tailwinds
Bruce 357R



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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by allsure
G'day Bob

I'm aware "special" manifold and exhaust system for the "S" engine, but my
budget does not run to actually buying them.

The local dealer suggests that they make about 4 hp difference. Perhaps when
I win "Lotto" I will buy them. Do you know of any going cheap?

Thanks for the advice regarding carby heat. I was not going to fit it as we
are not required to do so, but your simple idea could be used.


I did not know about the oil temp, but I will take your advice.

I really looking forward to get this thing in the air. Most of the painting
is finished ans final assembly begins!


Regards and thanks (again)

Ian Donaldson





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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by allsure
G'day Bruce357R

Thanks for the response.

Do you know if I can find Skystar online? I would like to see just what they
have to offer.

I have never used a Rotax engine and appreciate your tips. I am in fact
using a Warp Drive so I had better look at fitting springs on those carbs.

Regards


Ian Donaldson






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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by allsure
G'day again

I would like to see Bob or in fact any Rebel owner down here.

Australia is a great place to holiday. Very, very, unusual country!

If you are spending $US it is a very cheap holiday.


Regards

Ian Donaldson

----- >




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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by mike.davis
www.skystar.com
G'day Bruce357R

Thanks for the response.

Do you know if I can find Skystar online? I
would like to see just what they
have to offer.

I have never used a Rotax engine and appreciate
your tips. I am in fact
using a Warp Drive so I had better look at
fitting springs on those carbs.
Regards


Ian Donaldson

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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by Bob Patterson
Hi Ian !

Sounds like you're making great progress ! I'm sure you'll
love it when you get flying !

The intake manifold is not such a big deal, but the exhaust
really will help, both in noise and performance. What kind of tail
pipes (down tubes) did the standard exhaust come with ? The old
originals recommended automotive flex pipe - a really bad idea !
I switched long ago to a solid steel extension, also available
as automotive stock, and supported it with a ring of coil spring.
The '2 into 1' mufflers actually reduce power, but give a reasonably
quiet idle. Double up on the attach springs, as they create so much
backpressure that the muffler tends to blow right off the manifold
at full power, and sometimes sticks, hanging up on the flange,
making everything a LOT noisier, and damaging the bell shaped
connector. They are fairly loud at full power.

The 912S is well known for its "shake" - Kitfoxes were
shaking the carbs right off of the engines, until Rotax investigated
and suggested adjusting the rubber mounts a bit. It will be interesting
to hear how you make out, as I don't know of anyone yet flying the "S"
in a Rebel. One thing I do, that was recommended by the UL flyers,
is to add 2 pieces of safety wire to the air filters, pulling
forward. This helps keep them (and the carbs) on, AND prevents them
from disappearing out the bottom of the cowl, if they do get
shaken off. They also suggest running a piece of locking wire
through the inside of the exhaust springs, connecting the muffler
and the pipe, to hold the pieces somewhat together, in case the
spring breaks. (They do rust quickly !)

Have fun, and tell us how it flies !! (Skyrocket City !!!) :-)

.....bobp

-----------------------------------orig.-------------------------------
At 10:49 PM 9/7/01 +1000, you wrote:
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G'day Bob

I'm aware "special" manifold and exhaust system for the "S" engine, but my
budget does not run to actually buying them.

The local dealer suggests that they make about 4 hp difference. Perhaps when
I win "Lotto" I will buy them. Do you know of any going cheap?

Thanks for the advice regarding carby heat. I was not going to fit it as we
are not required to do so, but your simple idea could be used.


I did not know about the oil temp, but I will take your advice.

I really looking forward to get this thing in the air. Most of the painting
is finished ans final assembly begins!


Regards and thanks (again)

Ian Donaldson


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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by allsure
G'day Bob
-----


Progress! Maybe, but I'm sure sick of rubbing primer and paint! Painted it
bright white. Will be able to be seen from the moon!


The factory supplied flexible pipes. I like your idea of the solid tubes.

I have the 2 into 1 system, and will take your advice re the springs.


I will also double wire the carbs. Could spoil your day if a carb fell off!


As well as wiring the springs I also fill them with high temp silicone.
I have used this to great success on a 2 stroke I once flew. Really holds
the
bits in place.


Regards

Ian Donaldson




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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by Bob Patterson
Hi Ian !

Sounds pretty ! Hope you can upload a picture for us when
you get her all together....

The flex pipes leaked exhaust, and rusted VERY quickly - I
was constantly replacing them. You never knew when one was going to
crumble, as the inside rusted first. I mentioned the Canadian Tire
part number for the replacement, but that won't help you much...
I'm sure an auto parts store will have a similar pipe - it slips
over the muffler, clamped with a regular muffler clamp, and extends
below the cowl. I used an oversize strap clamp (just a strip of metal)
and wrapped a 1/4" dia. door spring around it several times to make
it stand off from the pipe. The strap clamp is fastened to the engine
mount by another rubber covered clamp. This setup reduces the heat
and lets the pipe move around to prevent cracking. Check the nuts
on the muffler clamp every D.I., as they tend to loosen.

The H.T. Silicone inside the springs sounds like a good
idea - stops them from buzzing.

Kepp going - it really IS worth it !!

......bobp

PS
I's LOVE to be able to come down & go for a flight - now
it's my turn to hope for the Lotto ! ;-)

-----------------------------orig.-------------------------------------------
At 12:11 AM 9/8/01 +1000, you wrote:
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G'day Bob
-----


Progress! Maybe, but I'm sure sick of rubbing primer and paint! Painted it
bright white. Will be able to be seen from the moon!


The factory supplied flexible pipes. I like your idea of the solid tubes.

I have the 2 into 1 system, and will take your advice re the springs.


I will also double wire the carbs. Could spoil your day if a carb fell off!


As well as wiring the springs I also fill them with high temp silicone.
I have used this to great success on a 2 stroke I once flew. Really holds
the
bits in place.


Regards

Ian Donaldson

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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by Legeorgen
Ian,

Try < Skystar.com >. They have started an online catalog but you may find
it more informative to call and talk to a real person. Ask for Dave Morris,
Their parts and service guy.

Bruce 357R



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Rotax 912 carb heat

Posted: Fri Feb 17, 2012 9:16 pm
by Legeorgen
Ian,

It's not likely that you would ever take off with a carburetor loss or
hanging in your 912S. They are knock out of their boots because of the
shaking on start up, do to the high compression cylinders and low mass weight
of the prop. They shake on any install although maybe more on some Kitfox's
due to the rubber mounts employed. Once knocked off, your engine would never
run long enough to depart your runway much less taxi to it! I know this from
personal experience.

Bruce 357R



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