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Rough Running 912
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kenryan

Joined: 20 Oct 2009
Posts: 426

Posted: Wed Dec 15, 2010 5:24 am Post subject: Rough Running 912

That example was for flying from a base of 7000 to 9000. I'm talking more about flying from sea level to about 14,000. Same answer?



On Tue, Dec 14, 2010 at 8:27 PM, Roger Lee <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)> wrote:

 [quote]--> RotaxEngines-List message posted by: "Roger Lee" <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)>

  

 I'm with Lucien. leave it alone. You will be a little rich for that flight, but so what it will fly just fine. Making a permanent needle adjustment should mean you are more or less permanently at altitude.

 

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KeysFox

Joined: 05 Jan 2009
Posts: 137

Posted: Wed Dec 15, 2010 5:44 am Post subject: Rough Running 912

My home bases are at sea level in Florida Keys and adjacent to Chesapeake

Bay but have flown over Grand Canyon, and around the South West Rockies up

to about 10,000 plus a trip Md to Fl at about 10,000 and have not noticed

any engine roughness in an early s/n 912. Can't remember going to 14,000

feet though.



BJ

KF IV N154K



  > That example was for flying from a base of 7000 to 9000. I'm talking more

 	  Quote: 	
		   about flying from sea level to about 14,000. Same answer?



 On Tue, Dec 14, 2010 at 8:27 PM, Roger Lee <ssadiver1(at)yahoo.com> wrote:



> 

> <ssadiver1(at)yahoo.com>

>

> I'm with Lucien. leave it alone. You will be a little rich for that

> flight,

> but so what it will fly just fine. Making a permanent needle adjustment

> should mean you are more or less permanently at altitude.

>

> --------

> Roger Lee

> Tucson, Az.

> Light Sport Repairman - Maintenance Rated

> Rotax Repair Center

> Home 520-574-1080  TRY HOME FIRST

> Cell 520-349-7056

>

>

> Read this topic online here:

>

> http://forums.matronics.com/viewtopic.php?p=323400#323400

>

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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Wed Dec 15, 2010 6:21 am Post subject: Re: Rough Running 912

 	  kenryan wrote: 	
		  I could easily be taking off at sea level and then flying to over 14000.



Ken Ryan

Anchorage, Alaska



	




I still think you'll be ok. By the time you get up there, you're going to be mostly wide open all the time anyway so the carbs should compensate pretty well. I've flown mine at density altitudes approaching 12,000' MSL without any visible running problems.



I would make sure that you have the carb vent lines installed correctly first (i.e. going into the aircleaners or airbox). The carbs really do go rich at higher altitudes if the vent lines are just hanging out in the breeze and that could cause problems that high up. 



LS

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kenryan

Joined: 20 Oct 2009
Posts: 426

Posted: Wed Dec 15, 2010 6:45 am Post subject: Rough Running 912

Thanks for the inputs!

On Wed, Dec 15, 2010 at 8:21 AM, lucien <lstavenhagen(at)hotmail.com (lstavenhagen(at)hotmail.com)> wrote:

 [quote]--> RotaxEngines-List message posted by: "lucien" <lstavenhagen(at)hotmail.com (lstavenhagen(at)hotmail.com)>

 kenryan wrote:

 > I could easily be taking off at sea level and then flying to over 14000.

 >

 > Ken Ryan

 > Anchorage, Alaska

 >

 >

 I still think you'll be ok. By the time you get up there, you're going to be mostly wide open all the time anyway so the carbs should compensate pretty well. I've flown mine at density altitudes approaching 12,000' MSL without any visible running problems.

 I would make sure that you have the carb vent lines installed correctly first (i.e. going into the aircleaners or airbox). The carbs really do go rich at higher altitudes if the vent lines are just hanging out in the breeze and that could cause problems that high up.

 LS

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Roger Lee

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

Posted: Wed Dec 15, 2010 8:21 am Post subject: Re: Rough Running 912

Ok, I didn't want to post this, but for the sake of no one messing with their engine here goes. I have friends that have been to 18'K + with their 912ULS and the clip at number 3. Leave your clips alone and your engine will take you any where you want to go.

I have several friends with their 912ULS fly regularly at 14K so don't give it a second thought.

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moosepileit

Joined: 10 Dec 2007
Posts: 26
Location: USA

Posted: Wed Dec 15, 2010 9:46 am Post subject: Re: Rough Running 912

Roger,



For the case of sea level to 14k'- I agree, CLIP #3, the standard for the 80HP Rotax UL.  My experience moving from 5k' to sea level proved that out.



You might want to look at the HACMAN for the case of going up high, less than $200 for the install, assuming you didn't need to send out the carbs for the tapping setup.



Now, My carb vents are just tucked in the bales from the float bowl.  I have the K&N filters, both pancakes, one per side, oriented properly.  Should I tap into the back plastic and run the carb vents back to the air filters?  Does anyone have a picture of this?  It would look just like running the vents to the air inlet manifold  on the ROTAX 912s that use a plenum/manifold connected to both carbs.

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Wed Dec 15, 2010 11:52 am Post subject: Re: Rough Running 912

 	  moosepileit wrote: 	
		  

Now, My carb vents are just tucked in the bales from the float bowl.  I have the K&N filters, both pancakes, one per side, oriented properly.  Should I tap into the back plastic and run the carb vents back to the air filters?  Does anyone have a picture of this?  It would look just like running the vents to the air inlet manifold  on the ROTAX 912s that use a plenum/manifold connected to both carbs. 	




I'd definitely fix this before flying at high altitudes. Soon as I can get out to the hangar with my camera, I'll take some pictures of how I did mine.



Basically, what you describe is pretty much it. Get two brass double-barbed fittings at Lowes or somewhere (1/8" IIRC), the fitting with barbs on each end and a disc in the center. I.e. looks like 



<<<<|>>>>



then, drill a hole in the back panel of each air filter (remove for this and clean out the scrap rubber completely). Push the barb in till it bottoms out at the disk. Push the carb vent line over the other end of the barb and you're done....



I have the big flat Rotax K&N's which makes this easy so sounds like you shouldn't have any trouble...



But I'll try to get some pics of what I have...



At my altitude (7000' MSL plus), this brought the full power EGTs up almost 100F, back to where they should be around 1250-1350....

LS

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moosepileit

Joined: 10 Dec 2007
Posts: 26
Location: USA

Posted: Wed Dec 15, 2010 12:31 pm Post subject: Re: Rough Running 912

Lucien, thanks!  I was fine cruising at 9500' msl w/ OAT about 32F/freezing.  Your description is great, thanks.  I don't think she'll be getting above a couple thousand feet for a while, EGT is 1400 WOT down low now and takeoff.



It makes sense to have the carbs as equal as possible, which does not include 2 vent hoses randomly in the  airflow, even just tucked against the carb bowl holders/bails.  



So, with this setup, is there any use for carb drip trays?  I don't need them for heat isolation and the carbs can't drip onto my exhaust in my kitfox...

Roger Lee

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

Posted: Wed Dec 15, 2010 1:15 pm Post subject: Re: Rough Running 912

Howdy Moose,



The vent lines need to be in the same general area so they pick up the same pressure to balance the carbs and if the engine were to shake hard for any reason sometimes you can get some fuel down them and that's why you don't want the vent lines on top of an exhaust and having a drip tray under them can help. The drip trays aren't there for the vent lines usually, but for things like a leaking float bowl gasket which can be common. I always keep a couple of float bowl gaskets lying around. Easy to replace. The drip trays provide a barrier between any fuel that comes out of a carb which is usually right above the exhaust. I would leave them alone. If you're flying you won't know the carbs are leaking until after you're on the ground and for many of us you won't know unless you pull the cowl.

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hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Wed Dec 15, 2010 2:04 pm Post subject: Rough Running 912

Roger,



What is your take on Lucien's idea of running the carb vent lines back into 

the air filters on a 912 UL?



Hugh McKay



--

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Wed Dec 15, 2010 2:57 pm Post subject: Re: Rough Running 912

 	  hgmckay wrote: 	
		  Roger,



What is your take on Lucien's idea of running the carb vent lines back into 

the air filters on a 912 UL?



Hugh McKay



-- 	




BTW, I didn't make this up. This requirement on the vent lines is in the installation manual for the 912 series. 



There's a diagram in there showing the lines being routed to nipples on the airbox for illustration purposes, but without the box you kind of have to invent your own method. Fortunately, it's easy to do.



Like I said, at my altitude my carbs definitely ran too rich before the fix (EGTs in the 1100's !) so I'm convinced! 



LS

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Roger Lee

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

Posted: Wed Dec 15, 2010 3:45 pm Post subject: Re: Rough Running 912

You can do it Lucien's way if you don't have a common airbox and it's ok, but if you have a common airbox it's better.



Kind of like one of those sayings:  not good, ok, better, best

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Tucson, Az.
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Cell 520-349-7056

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Wed Dec 15, 2010 4:44 pm Post subject: Rough Running 912

Lucien, I wasn't in on the discussion on the Kolb forum, but I took the time to read Section 15 and 16 of the installation manual and what it says is that the carb vents must be routed to a vacuum and ram air free zone. The air box supplies this, the air filter does not. Letting them just hang, secured by the float bowl bale is a perfectly acceptable option. 

Rick Girard

On Wed, Dec 15, 2010 at 4:57 PM, lucien <lstavenhagen(at)hotmail.com (lstavenhagen(at)hotmail.com)> wrote:

 	  Quote: 	
		   --> RotaxEngines-List message posted by: "lucien" <lstavenhagen(at)hotmail.com (lstavenhagen(at)hotmail.com)>

 hgmckay wrote:

 > Roger,

 >

 > What is your take on Lucien's idea of running the carb vent lines back into

 > the air filters on a 912 UL?

 >

 > Hugh McKay

 >

 > --

 For what it's worth, I didn't make this up. This requirement on the vent lines is in the installation manual for the 912 series.

 There's a diagram in there showing the lines being routed to nipples on the airbox for illustration purposes, but without the box you kind of have to invent your method.

 Like I said, at my altitude my carbs definitely ran too rich before the fix (EGTs in the 1100's !) so I'm convinced! 

 LS

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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Wed Dec 15, 2010 6:21 pm Post subject: Re: Rough Running 912

 	  rickofudall wrote: 	
		  Lucien, I wasn't in on the discussion on the Kolb forum, but I took the time to read Section 15 and 16 of the installation manual and what it says is that the carb vents must be routed to a vacuum and ram air free zone. The air box supplies this, the air filter does not. Letting them just hang, secured by the float bowl bale is a perfectly acceptable option. 



Rick Girard

	




Not at my altitudes it isn't. Fortunately 15.1 does clarify the issue a bit - it also says: 



"Pressure differences between intake pressure and pressure in the carburetor chambers may lead to engine malfunction due to incorrect fuel supply."



That effectively means the vent lines should be at the same atmospheric pressure (or in the same atmosphere) as the venturis. There is a pressure difference, tho pretty small, between the outside of the airfilter and the inside. So, if you have the choice, the lines really need to be routed to the inside. If you have the airbox, the requirement is very clear, with the diagram, etc.



Now, the interesting thing is it doesn't really show up at sea level. My plane was originally in Nebraska; the mixture was fine down there with EGT's up to about 1400 with the lines run down the sides into the bales in the usual way. I guess the effect isn't that significant there. So it's normally not a problem and the carbs still compensate pretty well. 



But when I got it up here after the ferry mission there was a BIG difference - my EGT's were barely out of the 1100's. And the plugs were starting to get fuel fouled after about the first 20 hours or so after getting it here. I later learned about the correct placement of the lines and after the mod that put the mixture back to practically normal. My EGT's run about 1250 to 1350, a lot closer to where they should be. Still slightly rich but definitely about the expected temps for my altitudes and no more fouled plugs. 



So in my view, it really is something you want to comply with if you fly at high altitudes. At sea level, yeah, it's probably not that big of a deal....

LS

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Dec 16, 2010 5:01 am Post subject: Re: Rough Running 912

FWIW, the standard vent line location for the Bing 94 CV carb on Jabiru engines, similar to the Bing 64 carbs on the 912 series, is to the inside of the K&N filter if the engine is not fitted with an airbox. Mine, and every other Bing 94 I've seen without an airbox, has a 90 degree elbow fitted into the end of the K&N filter with the vent line connected to that.



I know Jabiru and Rotax are different, but functionally, the Bing 64 and 94 carbs are essentially identical and require the same venting. Without an air-box, the only way to ensure the proper vent line location (in my opinion) is to route it into the filter. I would suggest it is even more important on a Rotax since they have two carbs with critical balance requirements.



I doubt seriously that this would cause rough running symptoms but it is a factor that should be dealt with properly, if for no other reason than to eliminate it from the mix of variables.

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hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Thu Dec 16, 2010 6:55 am Post subject: Rough Running 912

Thom, Lucien:



This discussion is very interesting. My 912 UL came new from Rotax with the 

carb vent lines neatly tucked behind the bowl clip and run down to just 

above the little pans under the carb bowl. I now have 400+ hours on the 

engine. I may be mistaken (or just ignorant of the fact) but to my knowledge 

Rotax doesn't address this issue at all. I fly from a field elevation of 

1035 ft. msl, and fly down to sea level on numerous occasions, and then at 

times up to 8500 ft. msl to cross over the Appalachian mountains. I have not 

had any obvious engine/carb problems that I know of. However I do notice 

that when changing plugs they seem to be too "black", and not the nice 

"brown" color everyone talks about. So Thom, if I am hearing you correctly, 

in your opinion I should route each vent line back into it's respective air 

filter. Did you do this on your old 912 UL (The Allegro 2000), and if so how 

did you do it? Did you ever operate the engine with the vent lines as they 

come standard from Rotax?



Hugh McKay



--

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Thu Dec 16, 2010 7:26 am Post subject: Re: Rough Running 912

 	  hgmckay wrote: 	
		  Thom, Lucien:



This discussion is very interesting. My 912 UL came new from Rotax with the 

carb vent lines neatly tucked behind the bowl clip and run down to just 

above the little pans under the carb bowl. I now have 400+ hours on the 

engine. I may be mistaken (or just ignorant of the fact) but to my knowledge 

Rotax doesn't address this issue at all. I fly from a field elevation of 

1035 ft. msl, and fly down to sea level on numerous occasions, and then at 

times up to 8500 ft. msl to cross over the Appalachian mountains. I have not 

had any obvious engine/carb problems that I know of. However I do notice 

that when changing plugs they seem to be too "black", and not the nice 

"brown" color everyone talks about. So Thom, if I am hearing you correctly, 

in your opinion I should route each vent line back into it's respective air 

filter. Did you do this on your old 912 UL (The Allegro 2000), and if so how 

did you do it? Did you ever operate the engine with the vent lines as they 

come standard from Rotax?



Hugh McKay



-- 	




Yeah, this is a little-known fact of the Bing 64's. Like I said, mis-installed lines don't seem to create a noticeable problem at lower altitudes. Also, since the airbox is often eliminated and filters only are used, it's just one of those installation errors that kind of goes unnoticed and isn't a problem most of the time. 



The installation manual is, of course, the oh-so-wonderful translation from German, so a lot of the wording in it just sounds strange and isn't entirely clear. But that blurb in 15.1 does describe the technical issue involved with the vent line installation and does clarify what to do sort of.



Now why Bing chose to design the carb that way, who knows. It seems kind of silly to me but carbs are kind of black magic anyway so I just follow the instructions and hope for the best .



BTW, as jetted from the factory, there's a rich spot in the 2000 to 3500 rpm range and the factory idle mix setting of 1.5 turns is, in my experience, overly rich (and WAY too rich at my altitude). So black plugs after an extended idle back to the hangar is kind of par for the course. After I got my rebuilt carbs back I spent about an hour on the idle mixture and ended up with about 3/4 turn out from fully closed. That helps, but doesn't eliminate a little bit of fuel fouling on the plugs.



The other thing besides temps that I look for is a nice, antique white baffle in the exhaust which indicates adequately lean running at full power. I check this with a flashlight at my post-flight every time.....



LS

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Dec 16, 2010 1:04 pm Post subject: Re: Rough Running 912

Hugh,

We ran our Allegro with vent lines tucked into the float-bowl bail too for the entire time we owned it, with no problems either. It is not essential to change that in any way as long as you don't have any really odd airflow under the cowl and therefore unusual pressure distributions. However, routing the vent line to the inside of the air filter is the way that Jabiru does theirs and it does eliminate any spurious pressure issues that might arise in some installations.



As Lucien said, black plugs are common after a few minutes of low rpm running. The only way to get an accurate plug reading on engines with Bing CV carbs is to cut the engine off at altitude at cruise rpm, do a dead stick landing and check the plugs. I am not recommending this, of course, though I have done it myself.

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hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Thu Dec 16, 2010 2:04 pm Post subject: Rough Running 912

Thom,

Thanks. Based on my operating experience and engine performance to date, I 

see no reason to start re-routing my vent lines. However, the information 

gleaned from the input from you and Lucien has been very helpful in better 

understanding the operating characteristics of the 912 UL.



Hugh McKay

Maiden, NC

Allegro 2000

Rotax 912 UL



--

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Fri Dec 17, 2010 6:58 am Post subject: Re: Rough Running 912

 	  Thom Riddle wrote: 	
		  Hugh,

We ran our Allegro with vent lines tucked into the float-bowl bail too for the entire time we owned it, with no problems either. It is not essential to change that in any way as long as you don't have any really odd airflow under the cowl and therefore unusual pressure distributions. However, routing the vent line to the inside of the air filter is the way that Jabiru does theirs and it does eliminate any spurious pressure issues that might arise in some installations.



As Lucien said, black plugs are common after a few minutes of low rpm running. The only way to get an accurate plug reading on engines with Bing CV carbs is to cut the engine off at altitude at cruise rpm, do a dead stick landing and check the plugs. I am not recommending this, of course, though I have done it myself. 	




BTW, another way that I mentioned before that you can do without pulling the plugs is just examining your exhaust baffles. What I've found is the high-power mixture will tend to be reflected in the baffles, but a rough gauge of what you're getting at low power settings will collect on inside of the exhaust outlet. 



I.e. the exhaust pipe will usually have a fair buildup of black soot but the exhaust baffle will hopefully be a light antique white. 



When I was doing my carb sync after getting my rebuilt carbs back a few months ago, I did a lot of running at idle and 2000 to 3000 on the ground. The baffle inside my exhaust got pretty tarred&feathered with soot. but after going up and doing a few touch and goes the baffles were nice and white when I got back down.



The other discovery is that when I finally got the idle mix set on the "knee", the idle EGT's ended up around 1050 to 1100F. I was at about 800 to 900F before, which I didn't know was just slobbering rich.... The idle speed also came up about 50 rpm as I leaned out the mix. 



Course this is all at my 7000' MSL and the density altitude is usually 8000' or more, so you kind of have to make adjustments like this up here. 



At sea level, you're pretty much just bolt the motor on and don't screw with it....



Oh PS: the fight I started on the Kolb list wasn't about the 912 vent lines (it was about the 2-stroke pulse line length).



LS

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