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[jabiruengines] EGTs and fuel quality

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Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Wed Apr 16, 2008 7:51 am Post subject: [jabiruengines] EGTs and fuel quality

Andy-

Being another windy, gusty day, I decided to look into making the  

ring and the guide vanes. (I have "before" temps that will suffice,  

but really wanted to get current figures)  Much to my surprise, when  

I got the carb and rubber sleeve off, I saw that there was a ridge of  

rubber between the carb side and the engine side. Maybe the rubber  

sleeve manufacturer foresaw this gap as being a potential problem,  

and decided to fill it. It is still not a perfect world, as the  

rubber ridge is about .018" (about 1/2 mm) smaller in diameter than  

the carb bore. That means it is about .009" lower all around than the  

carb bore...no big deal, in my estimation. On the other side of the  

ridge, though, the (I'll call it) adapter snout...the part that is  

held onto the splitter housing/intake manifold with 4 bolts, is about  

0.112" smaller than the ridge diameter, or 0.056" all around. This is  

where I will concentrate my efforts. I'll chuck up this piece, bore  

it to the carb diameter, and smooth and blend in this area. There is  

plenty of meat in this piece and I don't feel I will get anywhere  

near the groove in my efforts.



The other problem that I see is that the two components don't come  

close enough together to touch the ridge on either side. The  

impression of the two parts,the carb and adapter piece, in the rubber  

look like they miss contacting the ridge by maybe 0.020"-0.030". So  

there is that little area that could cause some turbulence, but not  

as much as it would be if the ridge weren't there and a large gap  

existed. I don't know if all the rubber sleeves are created equal, or  

whether some were built without the ridge, or if I could find a  

similar sleeve if/when I need one. I'll cross that bridge when I come  

to it.

Lynn Matteson

Grass Lake, Michigan

Kitfox IV Speedster  w/Jabiru 2200

flying w/490+ hrs

On Apr 15, 2008, at 4:25 PM, Andy Silvester wrote:



 	  Quote: 	
		   Lynn, Sounds like a good plan! I know others have tried without  

 much success

 with guide vanes upstream of the carb, so don't be too disappointed  

 if you

 can't get much from it. The theory is good, however! I don't know  

 about the

 successes gained by the poster on the Sonextalk forum; I'm not a  

 member and

 I didn't fancy joining just for one message. As you say, one thing  

 at a time

 and measure as much as you can, analysing afterwards on the ground.



 Cheers, Andy



 From: jabiruengines(at)yahoogroups.com 

 [mailto:jabiruengines(at)yahoogroups.com]

 On Behalf Of Lynn Matteson

 Sent: 15 April 2008 16:50

 To: jabiruengines(at)yahoogroups.com

 Subject: Re: [jabiruengines] EGTs and fuel quality



 Thanks, Andy. I was going to go up today and get some really good

 readings before I tore into the carb removal, ring building thing,

 but it was just too windy and gusty to get readings that would supply

 me with the "before" EGT's. Once I can get those, I'll go after the

 "gold ring." : ) I may even try some air-straightening vanes inside

 the tube just prior to the carb, but I want to do one thing at a time

 in order to know what did what.



 Lynn Matteson

 Grass Lake, Michigan

 Kitfox IV Speedster w/Jabiru 2200

 flying w/490+ hrs

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_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

andy(at)suncoastjabiru.co
Guest

Posted: Wed Apr 16, 2008 9:00 am Post subject: [jabiruengines] EGTs and fuel quality

Lynn,



OK, I'm a bit surprised by the existence of that 'ridge' as the ones I

inspected a while ago just had the two rounded ridges that locate in the

grooves in the carb body and the intake side adapter. In between there was a

gap, which I am suggesting filling. I guess the supplier changed the pattern

slightly. Also, it's really not the AIR we're interested in keeping out of

those spaces or grooves, it's FUEL. Remember, at around 12:1 - 14:1 air/fuel

ratio, it doesn't take much extra fuel to upset the ration big-time. As fuel

gets into that groove we think it swirls around due to air turbulence and

then exits back into the airstream in an uncontrolled way, meaning that

'splashes' of fuel are re-introduced downstream of the carb. These splashes

may-well form a liquid stream at some rpms and go down either the left or

right side of the splitter, causing the mixture imbalance. The idea of the

ring is to make as smooth a bore as possible right into the splitter from

the carburettor, so the mixture of fuel and air has a better chance of going

50/50 past the splitter. Any left/right EGT (mixture) differences would then

be due to turbulence or twisting of the air through the carb, and this could

be improved by the guide vanes. I recommend doing whatever's needed to

smooth-out the bore of the carb/coupler/adapter combination first, then

tackle any turbulence separately before the carb in the intake system. In

practice and if you have the right tool rake and cutting speed, you might

use a boring tool to remove the existing ridge inside the coupler, then you

have more space to fit a gap-ring. As always, more than one way to

accomplish the job but the result should be the same.



Hope this helps



Andy 



--

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Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Wed Apr 16, 2008 10:40 am Post subject: [jabiruengines] EGTs and fuel quality

I just got done boring out the adapter to the same diameter as the  

ridge in the coupler....about 1.672"...and blended the various  

machining operation marks out with a rubberized abrasive polishing  

"stone."  Now the carb, coupler and adapter are fairly smooth in  

transition, all being about the same diameter, give or take a few  

thousandths.

Next on the agenda is making the vanes. The pictures I've seen of the  

vanes show them as being short, but I'd really like to make mine  

follow the curve of the entire 6" long (measured right down the  

middle), 90° fiberglas tube that I made. In order to do it right, I  

might have to cut it in half...again...and insert the vanes, then  

'glass it back together again.

Lynn Matteson

Grass Lake, Michigan

Kitfox IV Speedster  w/Jabiru 2200

flying w/490+ hrs

On Apr 16, 2008, at 12:55 PM, Andy Silvester wrote:



[quote] 

 <andy(at)suncoastjabiru.com>



 Lynn,



 OK, I'm a bit surprised by the existence of that 'ridge' as the ones I

 inspected a while ago just had the two rounded ridges that locate  

 in the

 grooves in the carb body and the intake side adapter. In between  

 there was a

 gap, which I am suggesting filling. I guess the supplier changed  

 the pattern

 slightly. Also, it's really not the AIR we're interested in keeping  

 out of

 those spaces or grooves, it's FUEL. Remember, at around 12:1 - 14:1  

 air/fuel

 ratio, it doesn't take much extra fuel to upset the ration big- 

 time. As fuel

 gets into that groove we think it swirls around due to air  

 turbulence and

 then exits back into the airstream in an uncontrolled way, meaning  

 that

 'splashes' of fuel are re-introduced downstream of the carb. These  

 splashes

 may-well form a liquid stream at some rpms and go down either the  

 left or

 right side of the splitter, causing the mixture imbalance. The idea  

 of the

 ring is to make as smooth a bore as possible right into the  

 splitter from

 the carburettor, so the mixture of fuel and air has a better chance  

 of going

 50/50 past the splitter. Any left/right EGT (mixture) differences  

 would then

 be due to turbulence or twisting of the air through the carb, and  

 this could

 be improved by the guide vanes. I recommend doing whatever's needed to

 smooth-out the bore of the carb/coupler/adapter combination first,  

 then

 tackle any turbulence separately before the carb in the intake  

 system. In

 practice and if you have the right tool rake and cutting speed, you  

 might

 use a boring tool to remove the existing ridge inside the coupler,  

 then you

 have more space to fit a gap-ring. As always, more than one way to

 accomplish the job but the result should be the same.



 Hope this helps



 Andy



 --

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_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

andy(at)suncoastjabiru.co
Guest

Posted: Wed Apr 16, 2008 12:26 pm Post subject: [jabiruengines] EGTs and fuel quality

Lynn,



A picture's worth a thousand words! That coupler is different to the older

ones. Imagine the central ridge not being there, and that was where I

proposed the additional ring should be. It's a little disappointing to see,

as I was hoping for a big improvement in mixture distribution from your

efforts. Nevertheless, I still think the joints between the 3 parts have a

bearing on the way the fuel / air mixture (or more probably liquid fuel and

air separately) flows down the pipe. I like the idea of RTV as a gap-seal,

as long as it stays-put. The worst case scenario is that a sliver of sealant

gets sucked into a cylinder - so what? I doubt very much it would block

anything in the induction path or burn to form a hard piece causing damage.

Others here might think of something I haven't but for now, it seems like a

simple, cheap and effective solution. Once this is done if it makes

negligible difference, then it HAS to be the air flowing thro' the carb in a

helix, which we pretty-much knew anyway.



Cheers, Andy



--

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Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Wed Apr 16, 2008 12:56 pm Post subject: [jabiruengines] EGTs and fuel quality

Thanks, Andy....somebody at the coupling factory must have read your  

mind, because they sure made that gap go away. And just as we were  

going to get rich over building rings! : )



When I bored out the aluminum intake snout, that took an almost 1/16"  

mis-match in diameters out of the way of the airflow, so maybe a  

little was gained in looking into the gap situation, and perhaps not  

all the couplings ARE made with the gap-filling ridge, so it behooves  

owners to have a look and see.



I just slit my curved fiberglas tube down the middle, and will make  

vanes to insert before I close it up again. I'll take pictures as I  

go so if anybody wants to copy it...IF IT WORKS...they can. In the  

meantime, let the winds blow and the rains come...I'm down for a day  

or so. : )



Lynn Matteson

Grass Lake, Michigan

Kitfox IV Speedster  w/Jabiru 2200

flying w/490+ hrs

On Apr 16, 2008, at 4:23 PM, Andy Silvester wrote:



[quote] 

 <andy(at)suncoastjabiru.com>



 Lynn,



 A picture's worth a thousand words! That coupler is different to  

 the older

 ones. Imagine the central ridge not being there, and that was where I

 proposed the additional ring should be. It's a little disappointing  

 to see,

 as I was hoping for a big improvement in mixture distribution from  

 your

 efforts. Nevertheless, I still think the joints between the 3 parts  

 have a

 bearing on the way the fuel / air mixture (or more probably liquid  

 fuel and

 air separately) flows down the pipe. I like the idea of RTV as a  

 gap-seal,

 as long as it stays-put. The worst case scenario is that a sliver  

 of sealant

 gets sucked into a cylinder - so what? I doubt very much it would  

 block

 anything in the induction path or burn to form a hard piece causing  

 damage.

 Others here might think of something I haven't but for now, it  

 seems like a

 simple, cheap and effective solution. Once this is done if it makes

 negligible difference, then it HAS to be the air flowing thro' the  

 carb in a

 helix, which we pretty-much knew anyway.



 Cheers, Andy



 --

- The Matronics JabiruEngine-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:

http://www.matronics.com/Navigator?JabiruEngine-List

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

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