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912ULS: Carburettor and Airbox venting lines

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Martin Pohl

Joined: 30 Jan 2006
Posts: 118
Location: CH-8645 Jona SG, Switzerland

Posted: Sun Dec 16, 2007 2:56 am Post subject: 912ULS: Carburettor and Airbox venting lines

I am going to install the Rotax 912ULS in my CH601XL soon. The new installation manual from BRP-Rotax (Version 1 / Rev. 0, May 01/2007) is quite straightforward, nevertheless I do still have some questions:



- The manual states on page 92 that the carburettor venting lines should be routed into ram air or vacuum free zone or into the airbox. Drawing 59 shows the connection between carburettor vent and airbox. Ok, I understand that...



- Then the manual states on page 102 that the airbox venting line should be also routed into ram air or vacuum free zone OR INTO THE AIRBOX. Well, the drain is FROM the airbox, how comes that I should reroute TO the airbox???



What is common practice? Connect carburettor vent to airbox and then airbox vent to some place below?



Thank you for any advice!



Cheers Martin

CH601XL HB-YNA

_________________
Martin Pohl
Zodiac XL QBK
8645 Jona, Switzerland
http://www.pohltec.ch/ZodiacXL/Main.html

gfmjr_20(at)hotmail.com
Guest

Posted: Sun Dec 16, 2007 6:33 am Post subject: 912ULS: Carburettor and Airbox venting lines

Martin--

  I ran both my airox and carb vents separately down the engine mount into the slipstream.

  

 George May

 601XL 912s  174hours



 	  Quote: 	
		   Subject: 912ULS: Carburettor and Airbox venting lines

 From: mpohl(at)pohltec.ch

 Date: Sun, 16 Dec 2007 02:56:52 -0800

 To: rotaxengines-list(at)matronics.com

 

 --> RotaxEngines-List message posted by: "Martin Pohl" <mpohl(at)pohltec.ch>

 

 I am going to install the Rotax 912ULS in my CH601XL soon. The new installation manual from BRP-Rotax (Version 1 / Rev. 0, May 01/2007) is quite straightforward, nevertheless I do still have some questions:

 

 - The manual states on page 92 that the carburettor venting lines should be routed into ram air or vacuum free zone or into the airbox. Drawing 59 shows the connection between carburettor vent and airbox. Ok, I understand that...

 

 - Then the manual states on page 102 that the airbox venting line should be also routed into ram air or vacuum free zone OR INTO THE AIRBOX. Well, the drain is FROM the airbox, how comes that I should reroute TO the airbox???

 

 What is common practice? Connect carburettor vent to airbox and then airbox vent to some place below?

 

 Thank you for any advice!

 

 Cheers Martin

 CH601XL HB-YNA

 

 --------

 Martin Pohl

 Zodiac XL QBK

 8645 Jona, Switzerland

 www.pohltec.ch/ZodiacXL

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=152487#152487

 

 

 

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Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sun Dec 16, 2007 9:17 am Post subject: Re: 912ULS: Carburettor and Airbox venting lines

Hi Martin,



I have a Flight Design CTSW and the carb vent lines run into the airbox and all other lines from there run down and out under the bottom cowling just barely in the air stream. (oil vent line runs out at the same area)

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

Martin Pohl

Joined: 30 Jan 2006
Posts: 118
Location: CH-8645 Jona SG, Switzerland

Posted: Sun Dec 16, 2007 9:26 am Post subject: Re: 912ULS: Carburettor and Airbox venting lines

Thank you for your answers!



I was just wondering if it is a wise idea to run the pressure sensitive carb vent lines into the slipstream. Homebuilt.org and I think also Lockwood say it is not the best setup.



Nevertheless you don't seem to have troubles with this configuration. I will follow Roger's instructions.



Cheers Martin

_________________
Martin Pohl
Zodiac XL QBK
8645 Jona, Switzerland
http://www.pohltec.ch/ZodiacXL/Main.html

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sun Dec 16, 2007 3:45 pm Post subject: Re: 912ULS: Carburettor and Airbox venting lines

Hi Martin,



My hoses come down inside the cowling and actually stop right at the bottom. They don't actually protrude out into the slipstream, but right up to it.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

Martin Pohl

Joined: 30 Jan 2006
Posts: 118
Location: CH-8645 Jona SG, Switzerland

Posted: Mon Dec 17, 2007 9:36 am Post subject: Re: 912ULS: Carburettor and Airbox venting lines

Roger, that sounds fair! I will do it the same way.



Thx and cheers

Martin

_________________
Martin Pohl
Zodiac XL QBK
8645 Jona, Switzerland
http://www.pohltec.ch/ZodiacXL/Main.html

N601RT

Joined: 25 Feb 2006
Posts: 31
Location: Hillsboro, Oregon

Posted: Mon Dec 17, 2007 10:00 am Post subject: Re: 912ULS: Carburettor and Airbox venting lines

Martin and Roger,



(This is my first posting to this list. I've been lurking for a while.)



Be very careful of routing the carb vent lines. I personally saw a CH701 have significantly reduced power from routing the carb vent lines to the bottom of the cowl. Everything was fine during ground testing, but the plane would barely climb. Changing the vent line back to the original length solved his problem. There have been reports of others having problems with other installations where the vent line was improperly extended.



(Remember this is a vent line as you have properly discussed; It IS NOT a fuel overflow line.)



I took the Rotax Maintenance course at California Power Systems that Eric Tucker taught in early 2005. Eric stressed the importance of making sure the pressure at the vent line is the same as the pressure around the carb. He specifically said DO NOT extend the vent line to the bottom of the cowl as this has the chance of reducing the pressure the vent line senses and can prevent the carb slide from opening fully.



I've routed standard length vent line into a much larger tube which goes to the bottom of my cowl. There is about 3/4inch of the smaller line in the larger line. This allows any fuel that might come out of the vent line to flow into the larger line AND it allows the vent line to have the same pressure at the carb.



Regards,



Roy

N601RT: 2002 CH601HDS, nose gear, Rotax 912ULS, Arplast PV-50, All electric, IFR, equipped, 895hrs

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Mon Dec 17, 2007 5:07 pm Post subject: Re: 912ULS: Carburettor and Airbox venting lines

I agree that the vent lines are not supposed to be in the slip stream, but just down by the bottom of the cowling, but still inside should be fine.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

rparigor(at)suffolk.lib.n
Guest

Posted: Mon Dec 17, 2007 6:09 pm Post subject: 912ULS: Carburettor and Airbox venting lines

Just a note on 912/S:



Increase float bowl pressure over ambient pressure = richer mixture



Decrease float bowl pressure below ambient pressure = leaner mixture



As a matter of fact these guys sell a kit that allows you to decrease

float bowl pressure (lean mixture) by pulling a vacuum through a needle

valve (or automatic) via manifold cross over tube:

http://www.greenskyadventures.com/bing/HACmanorder.htm



Choose an area in cowl that is ambient pressure on ground and especially

in flight. One good location is just downstream of air filter, or go

measure chosen location on ground and in flight (climb, dive, go fast and

slow, flaps and clean).



Ron Parigoris



BTW 914 is a different beast, you need to vent float bowl to air-box

pressure (to accommodate turbo charging). As a matter of fact, for 115%

914 power operations the TCU rich-ens the mixture a little by plumbing

float bowl pressure via a solenoid from air-box pressure to above air-box

pressure (scoop in air-box airstream that increases pressure). None the

less theory of increasing float bowl pressure above some value to richen,

and decreasing float bowl pressure below some value to lean is the same as

912/S.



MAKE SURE FLOAT BOWL PLUMBING IS FREE OF RESTRICTIONS OR LEAKS ON ALL

9XXs.

Tommy Walker

Joined: 12 Jan 2006
Posts: 442
Location: Anniston, AL 36207

Posted: Sat Dec 22, 2007 4:08 pm Post subject: Re: 912ULS: Carburettor and Airbox venting lines

Roy,



Do you have a picture of your vent line setup that you could share?



Many thanks,



Tommy Walker in Alabama

N8701



 	  N601RT wrote: 	
		  Martin and Roger,



(This is my first posting to this list. I've been lurking for a while.)



I've routed standard length vent line into a much larger tube which goes to the bottom of my cowl. There is about 3/4inch of the smaller line in the larger line. This allows any fuel that might come out of the vent line to flow into the larger line AND it allows the vent line to have the same pressure at the carb.



Regards,



Roy

N601RT: 2002 CH601HDS, nose gear, Rotax 912ULS, Arplast PV-50, All electric, IFR, equipped, 895hrs

_________________
Tommy Walker
N25A - Anniston, AL

N601RT

Joined: 25 Feb 2006
Posts: 31
Location: Hillsboro, Oregon

Posted: Wed Jan 02, 2008 2:47 pm Post subject: Re: 912ULS: Carburettor and Airbox venting lines

Tommy,



Here is a photo of one vent line going into a larger line in my plane. I drilled a small hole in the top of the larger line near the end of the original length Rotax vent line, just to be sure the vent sensed the local pressure.



 (Sorry for the delayed response, I've been away for the holidays.)



Happy New Year



Roy

N601RT: 2002 CH601HDS, nose gear, Rotax 912ULS, Arplast PV-50, All electric, IFR, equipped, 895hrs

912 Carb Vent 4.1.jpg

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912 Carb Vent extension

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Martin Pohl

Joined: 30 Jan 2006
Posts: 118
Location: CH-8645 Jona SG, Switzerland

Posted: Thu Jan 03, 2008 12:03 am Post subject: Re: 912ULS: Carburettor and Airbox venting lines

Roy, thank you for sharing the photo of your venting line and your information about routing of the line.



Happy new year to all of you!



Cheers Martin

_________________
Martin Pohl
Zodiac XL QBK
8645 Jona, Switzerland
http://www.pohltec.ch/ZodiacXL/Main.html

Tommy Walker

Joined: 12 Jan 2006
Posts: 442
Location: Anniston, AL 36207

Posted: Thu Jan 03, 2008 3:54 am Post subject: 912ULS: Carburettor and Airbox venting lines

Roy,  

   

Thanks a lot.  I got the pictures and from what I can see you have a well put together engine.  Does the larger tube run down to the slip stream?  

   

Thanks,  

Tommy Walker in Alabama  

Do Not Archive  

   

       [quote][b]

_________________
Tommy Walker
N25A - Anniston, AL

N601RT

Joined: 25 Feb 2006
Posts: 31
Location: Hillsboro, Oregon

Posted: Fri Jan 04, 2008 6:43 pm Post subject: Re: 912ULS: Carburettor and Airbox venting lines

Tommy,



I ran the larger tube to the bottom of my engine mount, close to the firewall attachment. The tube does not extend below the cowl.



Regards,



Roy

N601RT: 2002 CH601HDS, nose gear, Rotax 912ULS, All electric, IFR equipped, 895hrs

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