jabiru air intake

[Guest alcol]

Hi guys

 

I have a j160 and I have changed the air cleaner to a sports pod the problem it is running rich at full power any surgestions

 

 

[Tomo]

Not enough airflow... i.e., to much restriction.

 

How do you have the balance tube hooked up?

 

If you don't mind me asking, why have you changed it to a pod filter?

 

 

[Guest alcol]

Not enough airflow... i.e., to much restriction.How do you have the balance tube hooked up?

 

If you don't mind me asking, why have you changed it to a pod filter?

Hi Tomo

 

I still have the 2inc scat hose conected to the carb heat box and pod to box.

 

There is no restriction I feel, I think the jab runs on a positive flow or o vac flow I lowerd the float a little bit better, I dont want to lower to mutch.

 

I dont understand balance tube. Cheers Alan

 

 

[Jaba-who]

Can you confirm a couple of things.

 

First what is a sports pod - i presume its some brand of filter.

 

What are it's figures for air flow and resistance etc?

 

Second - does 2200 have 2 inch scat as you suggested (ie SCAT 8) or is it supposed to be SCAT9 (ie 21/4 inch) like the 3300?

 

If you have SCAT8 and it should be SCAT9 then maybe thats the problem.

 

And I guess I am interested to know why you changed from the normal air cleaner. Was there a problem with it?

 

 

[Tomo]

Hi TomoI still have the 2inc scat hose conected to the carb heat box and pod to box.

There is no restriction I feel, I think the jab runs on a positive flow or o vac flow I lowerd the float a little bit better, I dont want to lower to mutch.

 

I dont understand balance tube. Cheers Alan

Okay, the tube I was thinking of runs from the air box to the carby, but if you have the pod connected to the air box it would still be connected. I'm pretty curious as to why you would fit a pod though?

 

 

[Guest alcol]

Can you confirm a couple of things.First what is a sports pod - i presume its some brand of filter.

What are it's figures for air flow and resistance etc?

 

Second - does 2200 have 2 inch scat as you suggested (ie SCAT 8) or is it supposed to be SCAT9 (ie 21/4 inch) like the 3300?

 

If you have SCAT8 and it should be SCAT9 then maybe thats the problem.

 

And I guess I am interested to know why you changed from the normal air cleaner. Was there a problem with it?

The Sport pod is a 3in necked down 2in that is what 2200 uses these pods are for use on 6 cyl engines so I would think it would suit my jab

 

I have made up a canister pod inside, with outside air pressure but still no good. the reason I moved the norm aircleaner I have put something in that space tool box and parts. It would not be smart to reduce a 3in to a 2in that would be looking for trouble, but I guess some people would. Cheers Alan

 

 

[Jaba-who]

Alcol, I am really sorry to do this and I know you are going to think I am a pedantic old knob but......

 

Can you answer the question again, in English, and actually say something technical and descriptive.

 

Sorry I am not trying to be smart or derogatory but I am trying to understand and work out what you are talking about.

 

I have googled Sports pod - no result, have never seen or heard of the term before and haven't seen one on a Jabiru engine before.

 

A pic would be good. When you say 6 cyl engines do you mean 6 cylinder Jabiru engines?

 

Specifically

 

1. WHAT is necked down from 3 to 2 inches.

 

2. Does a Sports Pod have a filter in it?

 

3. Do you know what the air flow features are? - Filter size?, flow maximal rate, surface area of the filter? Laminar or turbulent flow through it?

 

Then a further set of questions

 

What is now the nature of your induction system? From NACA duct to carby.

 

1 Is it longer, shorter or same length as original

 

2. Is it fairly straight or bent (& if so - how bent?)

 

Now crawling back in to my box

 

 

[Guest alcol]

Alcol, I am really sorry to do this and I know you are going to think I am a pedantic old knob but......Can you answer the question again, in English, and actually say something technical and descriptive.

 

Sorry I am not trying to be smart or derogatory but I am trying to understand and work out what you are talking about.

 

I have googled Sports pod - no result, have never seen or heard of the term before and haven't seen one on a Jabiru engine before.

 

A pic would be good. When you say 6 cyl engines do you mean 6 cylinder Jabiru engines?

 

Specifically

 

1. WHAT is necked down from 3 to 2 inches.

 

2. Does a Sports Pod have a filter in it?

 

3. Do you know what the air flow features are? - Filter size?, flow maximal rate, surface area of the filter? Laminar or turbulent flow through it?

 

Then a further set of questions

 

What is now the nature of your induction system? From NACA duct to carby.

 

1 Is it longer, shorter or same length as original

 

2. Is it fairly straight or bent (& if so - how bent?)

 

Now crawling back in to my box

Hi jaba I am not to much into the teck side of things a sport pod is a air cleaner made for sports cars turbo an alike and would suit 6-8 cyl cars.

 

necking down is reducing from 3inch to 2inch, hose from carb to filter a little longer and not a sharp bend. hope this makes a little clearer. Cheers Alcol

 

 

[Jaba-who]

OK.

 

Without any technical data it is difficult to say but.

 

What I meant was what physical piece of equipment is necked down? The Sports pod itself or do you have a joiner in the SCAT tube or is it from the NACA duct inlet to the SCAT tube.

 

It changes the flow physics if the necking down is smooth, abrupt, bent, or directly on either side of a laminar flow section of filter - lots of very significant changes occur at diameter changes and the results on air distribution can be quite dramatic.

 

3 to 2 inches is a big drop. It will cause a dramatic rise in velocity after the constriction. The velocity increase in that change may push your flow from laminar to turbulent which causes lots of changes in how it will pick up fuel and distribute it to the cylinders. Are you measuring CHT and EGT on all cylinders ?

 

The intake requires a certain amount of airflow to provide the right ratio/mixture with fuel at the carby. And the amounts for 4 and 6 or 8 cyl engines varies from engine to engine (based on many factors not just cylinder numbers - which is partly why if you go into Supercheap Auto and look at the air cleaner shelves there are dozens of different types) If the new filter (in your sports pod) tech stats differ much from the original then you may have not enough air getting through.

 

We did a lot of testing with several jab engines (2 x 3300s and a 2200) here and did a lot of changing filters, intakes and even developed a small scoop on the NACA duct duct to try to get the cylinder gas mix right. For various reasons I ran mine on essentially no filter for a long time (it had a very coarse foam filter soaked in filter oil to catch bigger stuff but not to impede air flow) but I changed it back to a RAF17 and installed a scoop to increase the inducted air.

 

But what we found was that the engines can show a dramatic changes with seemingly small changes in inducted air flow.

 

Ideally you should return your system to the standard, confirm it is working properly and then only if you have problems try changes.

 

But that may not be possible now so you may be left with just trying to get more air in. Put the tools in the cabin. :-) (Incidently what has a tool box in the nose done to the C of G))

 

A note of warning: I would not do anything unless you have CHT and EGT on all cylinders otherwise you have no idea what's happening.

 

You could try a small flange silastic-ed to the aft edge of the NACA duct (I have one that stands about 7 mm out) to drag more air in. Make sure it is made so if it detaches it can't enter the induction system!

 

 

[Guest alcol]

OK.Without any technical data it is difficult to say but.

What I meant was what physical piece of equipment is necked down? The Sports pod itself or do you have a joiner in the SCAT tube or is it from the NACA duct inlet to the SCAT tube.

 

It changes the flow physics if the necking down is smooth, abrupt, bent, or directly on either side of a laminar flow section of filter - lots of very significant changes occur at diameter changes and the results on air distribution can be quite dramatic.

 

3 to 2 inches is a big drop. It will cause a dramatic rise in velocity after the constriction. The velocity increase in that change may push your flow from laminar to turbulent which causes lots of changes in how it will pick up fuel and distribute it to the cylinders. Are you measuring CHT and EGT on all cylinders ?

 

The intake requires a certain amount of airflow to provide the right ratio/mixture with fuel at the carby. And the amounts for 4 and 6 or 8 cyl engines varies from engine to engine (based on many factors not just cylinder numbers - which is partly why if you go into Supercheap Auto and look at the air cleaner shelves there are dozens of different types) If the new filter (in your sports pod) tech stats differ much from the original then you may have not enough air getting through.

 

We did a lot of testing with several jab engines (2 x 3300s and a 2200) here and did a lot of changing filters, intakes and even developed a small scoop on the NACA duct duct to try to get the cylinder gas mix right. For various reasons I ran mine on essentially no filter for a long time (it had a very coarse foam filter soaked in filter oil to catch bigger stuff but not to impede air flow) but I changed it back to a RAF17 and installed a scoop to increase the inducted air.

 

But what we found was that the engines can show a dramatic changes with seemingly small changes in inducted air flow.

 

Ideally you should return your system to the standard, confirm it is working properly and then only if you have problems try changes.

 

But that may not be possible now so you may be left with just trying to get more air in. Put the tools in the cabin. :-) (Incidently what has a tool box in the nose done to the C of G))

 

A note of warning: I would not do anything unless you have CHT and EGT on all cylinders otherwise you have no idea what's happening.

 

You could try a small flange silastic-ed to the aft edge of the NACA duct (I have one that stands about 7 mm out) to drag more air in. Make sure it is made so if it detaches it can't enter the induction system!

Hi Jaba putting the jab aircleaner back is not an option dont worry about C-G you have wrote a lot of words but not mutch help but I thank you for that. One thing I learnt in my life if you have a problem you have to work it out your self. I will solve this and I will post results I have options up my sleave. A cht and egt on all cyl not an option but I will fit a AFR, you know that old saying nothing a german officer can not do.

 

 

[Jaba-who]

I agree that since all set ups are different you have to work it out for yourself. We found that all the engines we have here needed a different fix for what superficially appeared to be the same problem.

 

It is a bit concerning though that you plan to try to cure some problem without an effective means of measuring whether you are fixing or worsening the problem though.

 

But just to get back to the issue Tomo raised. If you have removed the jabiru hot air mixer box and the enclosed RAF17 filter and replaced them with the sports pod - where is the balance tube from the carburettor now connected? Or have I missed an answer to that question.

 

And secondly I am still trying to work out where the hot air scat tubing is connected into the system and how you open and close it?

 

 

[Guest alcol]

I agree that since all set ups are different you have to work it out for yourself. We found that all the engines we have here needed a different fix for what superficially appeared to be the same problem.It is a bit concerning though that you plan to try to cure some problem without an effective means of measuring whether you are fixing or worsening the problem though.

 

But just to get back to the issue Tomo raised. If you have removed the jabiru hot air mixer box and the enclosed RAF17 filter and replaced them with the sports pod - where is the balance tube from the carburettor now connected? Or have I missed an answer to that question.

 

And secondly I am still trying to work out where the hot air scat tubing is connected into the system and how you open and close it?

I have choped off the end of the aircleaner box with the hot air in take and cold intake and added a 2inc fitting to go to carb so use same as before, I have lowerd the needle a little and have solved the rich at full power problem,but after check of plugs it is still a little rich. I flew the jab yesterday and went ok just a little more ajustment and will get it right. When you say all the engines here are you a lame.

 

 

[Jaba-who]

I have choped off the end of the aircleaner box with the hot air in take and cold intake and added a 2inc fitting to go to carb so use same as before, I have lowerd the needle a little and have solved the rich at full power problem,but after check of plugs it is still a little rich. I flew the jab yesterday and went ok just a little more ajustment and will get it right. When you say all the engines here are you a lame.

OK I have worked out the hot air bit.

 

What about the balance tube (the tube that runs from the carby to the bottom of the hot air box) - where have you got that plugged in?

 

Am I a LAME - No.

 

And won't be insulted if you want to disregard everything I said/say because I am not. :thumb_up:

 

I have however been involved in rebuilding several Jab engines, been to a Jab engine course run by a LAME with Jab engine factory experience. We have three jab engines in my home town (2 X 3300s and 1 X 2200) which all had the well known problems of cooling etc (mine included) which I have been involved with doing a lot of work on. And we finally cured them all. So we have done a lot of work (with a lot of communications with Jabiru factory about it, mostly Don Richter) on cooling, airflows in and out of the carby etc etc. Rod Stiff has a property up here and has come to our hangar and given his two cents worth etc on a few occasions. We have produced some figures that Jabiru, we think, have used for design changes - but Stiffy will never admit to it

 

So take it how you want - I won't be insulted.

 

But I am still wondering about that balance tube - cos if that's not right it WILL make you run either rich or lean.

 

 

[Guest alcol]

OK I have worked out the hot air bit.What about the balance tube (the tube that runs from the carby to the bottom of the hot air box) - where have you got that plugged in?

 

Am I a LAME - No.

 

And won't be insulted if you want to disregard everything I said/say because I am not. :thumb_up:

 

I have however been involved in rebuilding several Jab engines, been to a Jab engine course run by a LAME with Jab engine factory experience. We have three jab engines in my home town (2 X 3300s and 1 X 2200) which all had the well known problems of cooling etc (mine included) which I have been involved with doing a lot of work on. And we finally cured them all. So we have done a lot of work (with a lot of communications with Jabiru factory about it, mostly Don Richter) on cooling, airflows in and out of the carby etc etc. Rod Stiff has a property up here and has come to our hangar and given his two cents worth etc on a few occasions. We have produced some figures that Jabiru, we think, have used for design changes - but Stiffy will never admit to it

 

So take it how you want - I won't be insulted.

 

But I am still wondering about that balance tube - cos if that's not right it WILL make you run either rich or lean.

No you sound that you have had a lot to do with jabs any info is good I am a auto mechanic aircraft engines are a little differant but same princable.

 

i know its a bit hard to explain the flap box has 3 inlets 1 comes from carb 1 from air cleaner 1 to hot air exhaust, hope this is clearer pull hot air /close cool air to carb.

 

 

[Jaba-who]

OK, I think I have it.

 

One important bit here is the thin tube from the carby to the flap box (Balance tube).

 

It sounds like it is possible it may be OK but still not completely sure.

 

In the standard Jabiru set up - that tube enters the hot air mixer box near the bottom well away from the air entry and and the pressure in the box is transmitted down the tube to the carby. When the pressure drops (at high altitude) it causes the pressure in the carby top chamber to drop and that moves the diaphragm in the top chamber of the carby and that moves the main needle to adjust the fuel flow - hopefully at just the right amount to compensate for the the altitude change.

 

Now in your set up - PROVIDED the pressure changes are the same in your new, smaller box and PROVIDED the air flows are not interfered with it may not have a wrong effect. But when you change the shape of the box you do two things:

 

1: Change the shape of the airflow through it

 

2: Change the pressure at different points (especially before and after constrictions or bends.

 

So if your new point where the balance tube is joined is at a high or low pressure spot it will change how the tube effects the carby. That could make it run rich or lean.

 

Also if the flow is turbulent it may distort how the air enters the carby and how it then distributes the fuel:air mixture.

 

Jabiru found that even small changes in shape, like sharp bends, rough surfaces all made turbulence and distorted airflow in the big, full size airbox. They make a big point of telling builders to ensure all bends are smooth and of as big a radius as possible with no sharp edges etc.

 

Making a small box might have different airflow through it (maybe worse, maybe better, maybe same - I don't know) and just attaching the balance tube to that small box might not have the same result it would have had in the full sized airbox.

 

I guess its hard to suggest fix-its when there are so many variables.

 

 

[Guest alcol]

OK, I think I have it.One important bit here is the thin tube from the carby to the flap box (Balance tube).

It sounds like it is possible it may be OK but still not completely sure.

 

In the standard Jabiru set up - that tube enters the hot air mixer box near the bottom well away from the air entry and and the pressure in the box is transmitted down the tube to the carby. When the pressure drops (at high altitude) it causes the pressure in the carby top chamber to drop and that moves the diaphragm in the top chamber of the carby and that moves the main needle to adjust the fuel flow - hopefully at just the right amount to compensate for the the altitude change.

 

Now in your set up - PROVIDED the pressure changes are the same in your new, smaller box and PROVIDED the air flows are not interfered with it may not have a wrong effect. But when you change the shape of the box you do two things:

 

1: Change the shape of the airflow through it

 

2: Change the pressure at different points (especially before and after constrictions or bends.

 

So if your new point where the balance tube is joined is at a high or low pressure spot it will change how the tube effects the carby. That could make it run rich or lean.

 

Also if the flow is turbulent it may distort how the air enters the carby and how it then distributes the fuel:air mixture.

 

Jabiru found that even small changes in shape, like sharp bends, rough surfaces all made turbulence and distorted airflow in the big, full size airbox. They make a big point of telling builders to ensure all bends are smooth and of as big a radius as possible with no sharp edges etc.

 

Making a small box might have different airflow through it (maybe worse, maybe better, maybe same - I don't know) and just attaching the balance tube to that small box might not have the same result it would have had in the full sized airbox.

 

I guess its hard to suggest fix-its when there are so many variables.

Ahh now I know what you mean yes I did have it in the box and it was no good so I vented it to the cockpit as per rod JABIRU I checked carb 280 needle jet 225 main jet scribed on carb but I HAVE A 245 MAIN I will drop it down to 235 main I think needle jet is 290 and drop that down 280 I flew it again saturday slill a little ritch. But still have not received jets next week hope.

 

 

[Jaba-who]

OK back to some more specific qestions:

 

How are you deciding it is a bit rich?

 

What monitoring do you have?

 

You said it is running rich at full power.

 

Do you think it is running rich on the ground/at low altitudes/or at high altitudes/at all altitudes.

 

 

[Guest alcol]

OK back to some more specific qestions:How are you deciding it is a bit rich?

 

What monitoring do you have?

 

You said it is running rich at full power.

 

Do you think it is running rich on the ground/at low altitudes/or at high altitudes/at all altitudes.

its ritch after take off flutering 300 ft I know this about 2 years ago the same thing I rang jab and they said check float level and air element it looked good but i changed it and ok, I have only reached 1000 ft so dont know I feel that the main jet has allways bean to big It must have run on the brink or just on the edge of not ritch since I have had this jab. I think jabiru jet them on the edge as to keep the heads cool, and I am waiting for the AFR gauge to arrive and that will tell me a bit more.

 

 

[Jaba-who]

You are right that Jabiru advise to use the bigger jets to keep them cool but they have not always had bigger jets in them so you would have to check the sizes you have to be sure yours has them - it may not.

 

I am not sure what you mean by "flutering" - but suspect you mean what we might call spluttering or maybe "missing". Fluttering to me anyway is not usual term for engine noises so I am not sure I have it right.

 

That is one cylinder doesn't fire so you get very short stop-start sounds. As a result the engine runs a bit rough.

 

I am going to assume thats what you mean and you can correct me if I have it wrong.

 

So apart from Jabiru's advice how have you confirmed it is running rich?

 

Missing/Rough running does not always mean it is rich

 

It could be from:

 

1: All cylinders running rich

 

2:All cylinders running lean

 

3: (More likely) Some running rich and some running lean (or some running OK).

 

Number 3 is more likely because that is what Jabirus are famous for.

 

In fact Jabiru now recommend builders do some specific things to fix this. Either baffles in the cobrahead (part of the tube INTO the carby) or something new that is not yet a proper recommendation but probably will soon - they have designed a new plenum chamber (the part AFTER the carby) but as yet I think they are only developed for the J3300 (I could be wrong there). That part is available - costs $600AUS and may become a recommended change before too much longer. They recommend these for stopping the wide spread of temperatures that happens - but it does this by making the fuel:air mix more even.

 

But the cobrahead fix is something you could try - but it is possible that you may not get the full information needed without monitoring all cylinders as I said before.

 

By the way I am not familiar with the abbreviation AFR - What is that?

 

Have a look at http://www.jabiru430.com/EngineCoolingimages.html

 

 

[Suitman]

Ummmmm Air-Fuel Ratio???

 

 

[Guest alcol]

Ummmmm Air-Fuel Ratio???

AIR FUEL RATIO GAUGE

 

 

[Jaba-who]

Ok that makes sense. Should have picked it.

 

Where does it sample from?

 

From the exhaust pipe or is it taking from somewhere before the cylinders or at each cylinder outlet?

 

Been at the airshow in Bundaberg for two days Just spent some time talking with an engineer from the engine manufacturers. He was saying they feel the new plenum chamber is not the full answer. Works a bit but the best results are from altering the inlet flows to the carby. Also reminded me of the other "mod" which i did which is simply tilting the carb toward the rich side. That also narrowed down my temp ranges quite bit.

 

He explained the physics of why that works, which was interesting.

 

Anyway I'd be interested to know what your AFR readings are?

 

 

[Guest alcol]

Ok that makes sense. Should have picked it.Where does it sample from?

 

From the exhaust pipe or is it taking from somewhere before the cylinders or at each cylinder outlet?

 

Been at the airshow in Bundaberg for two days Just spent some time talking with an engineer from the engine manufacturers. He was saying they feel the new plenum chamber is not the full answer. Works a bit but the best results are from altering the inlet flows to the carby. Also reminded me of the other "mod" which i did which is simply tilting the carb toward the rich side. That also narrowed down my temp ranges quite bit.

 

He explained the physics of why that works, which was interesting.

 

Anyway I'd be interested to know what your AFR readings are?

I have welded a o2 sencer at the head of 2inch exhaust near 4 into one muffler works good. Reading ritch at full power and no fluttering as before as I level out it drops back into the optimal range when I decend it reads lean. it is very sensitive on cruise tilt the stick up a bit and it reads ritch tilt down and it drops to optimal without throtel ajustment. Flew a few hours on weekend looks good I intend to do some further mods later will keep posted, I think its a simple equation air intake 100% fuel 20% if the air is less then you must lower fuel ie 90% air then 15% fuel it seams to work for me the end result a slight loss of horse power.

 

 

[Guest alcol]

Ummmmm Air-Fuel Ratio???

Ok 235 main jet lowerd needle 16th inc at this time all is good done 2 hours AFR good checked plugs ok. I need a longer needle at the top what is the differance with 6 cyl needles are they a differante profile, I need a little longer. I will do some further mods to air cleaner later.

 

 

[Jaba-who]

Now you are in the carby - I have to stop giving suggestions. I have done a lot of reading (buy the Bing Carby manual and read that - a lot) but I have no experience with changing the needle lengths or positions.

 

Best of luck.