Bing Carby Mods to improve EGT Spread

[JabSP6]

I was just reading a forum where in France you can send your carby to a company and they modify the Emullsion Tube by drilling it out and this supposedly improves the fuel atomisation which in turn is supposed to improve the EGT spread. They swear by it and it only costs around $40 Aus plus freight. I know a few people in Aus have mentioned this and i was wondering if anyone has tried this and can shed some light on exactly what is done. A diagram of the location of the emmulsion tube and a drill size would be much appreciated. I had heard of drilling out the choke jet located in the bowl to improve cold starting, but i don't have this problem. Very interested to hear if anyone has done this mod and verified the results. I can also verify that Jabiru are now also trialling the cross in the air box to improve the EGT spread with their new inlet manifold. Hopefully they will come up with a solution that will cure this problem for all jab motors no matter what version engine or type of plane they are in.

 

Wags

 

 

[facthunter]

Any thing that improves the atomisation of the fuel would help. If it was a gas you would have less of a problem, and it might actually cure it completely. ( Would be interesting to run one on lpg and see how it affected the spread.). Ground test. I wouldn't suggest flying it at this stage.

 

From memory the emulsion function is part of the mixture control but does break up the fuel stream into smaller drops. I can't see it entirely overcoming the problem, because you won't get complete atomisation in the carb, but IF it helps check it out. It is easy to make claims though.

 

Designing a manifold to get EVEN air and mixture is very difficult. The 0-200 Continental has the carb mounted up-draught underneath the motor and that is EASIER to get right. Not many updraught/updraft carbs around. Nev

 

 

[xair1159]

It was on the French Jabiru forum, but the company doing the mod is in South Africa, see the attached SB. My French is schoolboy level, but with Mr. Googles help it looks as though they drill out the atomiser which is the bit the needle sits in, not the emulsion tube. I could be wrong though...

 

Same company is also doing a mod to the hydraulic lifters.

 

Nick

 

Shadow_Lite_SL7_Fuel_Distribution_14December.pdf

 

Shadow_Lite_SL7_Fuel_Distribution_14December.pdf

 

Shadow_Lite_SL7_Fuel_Distribution_14December.pdf

[JabSP6]

Nick

 

That is the bulletin i have seen. I was just wondering if there is any way of contacting the company that does the mod to find out exactly was is done. Hopefully if we can try this mod and it works it will help solve a lot of issues and then we can work on tuning the carby to get the optimal power and ecconomy with nice even EGT's across all cylinders.

 

Wags

 

 

[xair1159]

Wags,

 

Try "hadow Lite now trading as Jabiru SA"

 

http://www.jabiru.co.za/

 

Let us know how you get on.

 

Nick

 

 

[Vev]

SP6,

 

For the 6 cyl only (doesn't work on the 4) ... drill the emulsion tube out from 2.5mm to 3mm and drill the air hole from the mouth of the carby using a 3/16. To further improve the EGT/CHT spread remove the manifold divider and replace it with a 12mm round. The carby mod came from the South Africans and has been tested but Jab in oz .. it works well.

 

Cheers

 

Vev

 

 

[Guest 4aplat]

I had heard of drilling out the choke jet located in the bowl to improve cold starting

I think the weather is colder in France than in Australia ......

 

but why do you want to drill the choke jet ? You just have to change it !

 

you could find it at a BMW motorcycle dealer

 

MicheL

 

 

[JabSP6]

Vev

 

This is the info i was looking for. Thankyou. Can you just clear up 2 things for me please. I am looking at the diagram of the Bing Carby in the Service Bulletin JSB 018-1. You are suggesting to drill out the emulision tube to 3mm, Is this what is shown as the atomiser? You also suggest to drill out the air hole to 3/16", Is this the air density sense port? Sorry for being a pain but i just want to make sure i have it right before i carry out this modification.

 

Once i have this info right in my head i will do this mod on the weekend and will report results on this thread. At the moment at cruise i have a difference of around 90 degress C but averaging around the 680 degrees C area. Wide open throttle gives an average of around 40 Degrees C lower.

 

Wags

 

 

[Vev]

Hi SP6,

 

No probs ... the answer is Yes and Yes

 

You can tell the emulsion tube as it has 4 holes at 2.5mm in the side of it ... you cant mistake it when you have it in your hand. Yes the air density sense port is the one, however be careful when you drill it as its a big hole.

 

Cheers

 

Vev

 

 

[jetjr]

So is this mod being done to new Jabs from Bundy?

 

 

[facthunter]

Surely all this will tend to lean out the mixture. Wouldn't you have to correct that with adjustments to the needle and Main Jet ....Nev

 

 

[Vev]

Nev,

 

I guess it has the potential to very marginally lean the mixture but it's small beer, it more about improving the atomisation of the fuel ... never the less it still needs to be done in conjunction with the recommended jetting as per the attached bulletin released in 2009 to increase the fuel mixture.

 

http://www.jabiru.net.au/Service%20Bulletins/Engine%20files/JSB018-2.pdf

 

This mod was shown to me when I did the engine course at Jab 6 months ago.

 

Cheers

 

Vev

 

 

[facthunter]

The link is usefull, with all the data After a less than complete examination, I would question a couple of points. The effect of the loading of the prop is mentioned but then says that the static (or ground) rpm will have the same effect as the inflight situation. ?????

 

It also states that the idle system mixture affects the whole range. Well it IS open but there is little or NO pressure differential to make it work when the butterfly is open. The choke system is similar. The choke is ineffective when the throrrle is open. They are both a bypass system.

 

I would like to refer also to recent finding by the FAA in the states where an in flight engine failure of a Jabiru engine was attributed to the dashpot sticking OPEN. The report stated that the engine would run excessively RICH because the needle would be wide open. ANY tuner of SU, Stromberg CD bings or even AMALs would know that the opposite is the case. IF the slide jambs open, the fuel will NOT come out of the jet because the pressure drop is not there. Without a difference of pressure from one side of the "dashpot" to the other, it will NOT open. This effect replaces the "venturi" in normal carburettors, as a means of "pulling" the fuel through the jet. When we are dealing with carburetters, it is a good idea to understand how they function. Regarding the effect of the float level on the mixture, it WILL affect the mixture, the amount of the pressure drop through the carburetter determines whether this will be a large or a small effect . With a reasonable pressure drop, the main determinant of fuel flow will be the area of the jet orifice. If you don't have a reasonable pressure drop the tuning of the carb. becomes very imprecise requiring LARGE jet sizes to get the fuel flow.

 

. Nev

 

 

[Vev]

Hi Nev,

 

I quite agree ... the idle system and choke do very little in terms of fuel contribution when the butterfly is open ... a mistake often made is to have the idle set too high and the choke system not work on start up as the throttle (butterfly) needs to be all but closed to create the pressure drop to work the choke and idle systems.

 

Again I agree ... float levels are important in terms of mixture control and they need to be checked to ensure they remain constant during routine servicing. The Bing has its subtle characteristic and understanding the different needle and seat compound combos and sizes is important to manage float levels.

 

Interesting observation on the FAA finding ... someone there obviously doesn't understand how a CV carby works!

 

Cheers

 

Vev

 

 

[deadstick]

Has anyone seen the new 3300 manifold? I am chasing an image to see what has changed, as during a discussion the Jab rep at Avalon he stated that Rod was seeing even EGT spreads across the board and CHT's within a b's DK of each other so whats different?

 

 

[JabSP6]

Deadstick

 

I haven't laid eyes on the new manifold yet mate but a good source at the factory tells me that they are still not seeing even EGT's across the board with this new manifold. This is why they have not released them yet. In fact they are now experimenting with a cross in the inlet manifold which has been documented on other jab sites to try to improve the spread in conjunction with the new manifold. They are trying different lengths and different positions to come up with a fix. We will have to wait and see i guess.

 

Cheers

 

SP6

 

 

[jetjr]

Talking to them late last week, the cross is still the best fix they have. "It may go into production models shortly"

 

It will be fitted in the outlet of the air cleaner housing, needs to be ~ 25mm long

 

This has been experimented on for some time there. Theres nothing new here, even this solution is a "maybe" fix. Jab Ok to admit they havent solved the issue completely yet but this might help.

 

 

[facthunter]

You want to bear with Jabiru here. Getting the same mixture strength to each cylinder with a carb is a "black art". ALL single entry fuel systems have the same problem. On auto's it just costs fuel (reduced efficiency) because the engines don't sit on 75 t0 80% power they don't exhibit the temp criticality that air cooled aero engines do. If the fuel vapourised completely in the carb most of the problem would not exist. (but that is close to impossible to achieve). Nev

 

 

[Modest Pilot]

An unexpected increase in manifold pressure turned out to be a minute crack in the tube at the take off point. It's located right under the butterfly valve. Interestingly the EGT spread narrowed to 10-15F, with a minute increase in overall temp's. Jabiru think it maybe turbulance create on the opposite side of the carb from outlet of the atomizer. It gave a constant 3" less reading accross the cruise/climb range. Jab are still working on the new manifold at this stage you will likely need new or modified inlet pipes to fit it.

 

 

[facthunter]

i would suggest that they are right. Extra turbulence gives better atomisation/ evaporation, and your mixture spread reduces. Nev

 

 

[deadstick]

 

 

 

 

 

 

 

 

 

[Vev]

Hi Deadstick,

 

Many thanks for posting ... I have heard good things about it and hope it delivers all that is has promised.

 

I am curious what if anything they have done with divider aerofoil in the plenum chamber, has this been changed too?

 

Will you be making the carby mods as well?

 

Cheers

 

Vev

 

 

[jetjr]

I assume this needs new intake tubes too?

 

Looks expensive, suprised they dont have flow straightener incorperated?

 

 

[Modest Pilot]

Hope I'm wrong but the plenum chamber still looks on the small size. My J230 is updated as follows: 290 needle jet and new needle to match, flow straightner, and the biggee 3/16" equalizer vent and 3mm emulsion tube holes. The latter brought the EGT range down to 650-680 F at 2800 rpm 20" MP and 23lt/hr with a Senesnich 56" pitch prop. at 2000' and 23 deg OAT. T/O really gets up and goes @ 42 lt/hour F/F and even lower temps. Had to reset the idle down from a little over 1000rpm; Seems smoother from 850 rpm-3300rpm than before. Starts going rough below 800rpm. So unless the new plenum offers a huge improvement I think that wraps up my tuning efforts for a while.

 

 

[facthunter]

The EGT spread will be the crucial test. I can't see the principle in the design myself. All I know is practically every engine that feeds a single carb into any simple manifold has giant trouble getting mixtures even. I wish them luck as there is obviously a lot of effort expended in producing it. Nev