Carburettor emulsion tubes
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  1. #1
    1000+ Posts Dave's Avatar
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    Default Carburettor emulsion tubes

    Hi guys,

    I have been searching for days for a chart or some sort of information as to the different emulsion tubes available for weber carbs and their characteristics.
    I currently have an F45 in the primary and it is too lean at low to mid revs.



    Dave

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  2. #2
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    Dave,
    From the number you quoted I assume you are using a DGAV or similar. You will find it almost impossible to find a suitable chart that makes sense. The emulsion tube is more or less a fuel brake for higher revs and it is very difficult to detect changes in tubes at the revs you are talking about. I have not tried an F45 but I am using an F50 and an F66 in different 504s. I did pull apart a new Weber especially set up for a 504 and it ran an F2 in the primary. To quote the Weber book, "the chaotic emulsion tube identification system....and you have all the elements of a good mystery ". Most people go with the tubes that came with the carby and "play" with the main and idle jets. The idle jets are really important up to about 2000 rpm when the progression circuit cuts out. If you have a set of DCOE s, disregard some/most of the above. Good luck.

  3. #3
    1000+ Posts Dave's Avatar
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    Thanks Bob,

    The carb is a Weber 34/34 Drtc 15/100
    I'll keep looking into it,


    Dave


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    Howdy Bob and Dave,

    My understanding (and I'm not doubting that you have more experience in Webers, Bob!) is that the emulsion tube profiles the mixture, where it's actually the air corrector in the end of the emulsion tube that 'brakes' the fuel, otherwise the mixture would run excessively rich at higher revs. From what I've picked up, the emulsion tube rarely needs to be changed once you have the right one for the engine - that is, they have a pretty wide scope for engine mods before you have to change the tube. I suppose that's sort of what you're saying...

    Stuey

  5. #5
    Fellow Frogger! AlsPug504's Avatar
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    Icon4 Re: Emulsion tube function

    The emulsion tube actually controls the mixture volume! Their primary function is to aerate the fuel in the Fuel well (That is the passage the emulsion tube sits in)

    As vacuum is applied to the port, slot, or venturi. Depending on what circuit it operates on. Fuel is siphoned from the bottom of the well.

    As the level in the well drops the holes on the side of the emulsion tube are uncovered, and allow air in. The stronger the vacuum the more holes are uncovered, and so the greater the Emulsification is. Hence the reason it is called mixture volume because it literally increase the volume of mixture (mixture being defined in this case as the frothed fuel). It also diffuses the vacuum being applied to the fuel so as to reduce the amount going into the engine. This balances the pressures between the float bowl and the venturi.


    As for your problem with the weber? trial and error is the only real solution. Basicly you want the largest quantity of air availiable passing through the emulsion tube. Which is controlled by the jet in the top of the emulsion tube.

    A basic rule is: The higher the vacuum applied to the well in question the lower down the holes will have to be and conversely the lower the vacuum the higher up the tube the holes have to be.

    If this were the idle circuit, the holes lower in the tube will control the idle and the ones higher up control off idle.

    At each rpm point, say idle try an emulsion tube with more holes at the bottom of the tube till the engine stumbles. Gradully work up the rpm range doing the same. The stumbling or leaness is when the airbleed can no long improve the frothing.

    I would advise that you tackle fuel jets first! Get them right. Their is no point even touching emulsion tubes till the fuel jets are correct. Which i suspect is probably were the leaness is coming from.

    I would recommend that you work on one circuit at a time! Blocking off the other circuits that cut in latter in the throttle opening, if you can.

    Hope that is of some help.

    Al

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    Member 750sport's Avatar
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    Here goes.....the greatest simplification of Weber carb tunning ever....

    If off idle (up to about 2000 rpm as mentioned earlier) is good you can leave the idle jet out of the equation.

    Lean running at mid throttle is too small a main jet, richen it up with a larger jet size (usually attached to bottom of emulsion tube), if it becomes too rich at WOT reduce the size of the air corrector jet (usually attached to top of emulsion tube) the reverse for lean. You will almost never need to change an emulsion tube from the original fitted to the carb by the factory.

    Confirm setting with plug reading if you are old school or a wide band O2 sensor if you are new age.

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    I am truly impressed at the level of detail and largely factual info on this thread. Just to add a comment on emulsion tubes, the Weber numbering mostly means nothing and stock or factory fitted emulsion tubes should not be changed. If it is necessary to change the emulsion tubes then such an activity must involve a dyno and gas analyser and a knowledgeable operator.

    The jets on the other hand can be done by a back yard hack using things like driveability, colour of plugs etc All things being ideal the issue you describe is classic main jet too small symptoms, I suggest you could open the jet up by .05mm increments and see what happens.

    At this URL there is a Weber Jetting table http://members.efn.org/~msayer/weboem.html
    OddfireV6
    504 V6 24V, 203

  8. #8
    1000+ Posts Dave's Avatar
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    Thanks for all your help guys, i have tried many combinations of bigger mains and different air correctors. The problem is that under acceleration it leans off, but is rich at other times. Putting a bigger main jet just makes it run richer and richer in all conditions but it still leans out when accelerating from a rolling start. I dont think this problem occurs above 4000rpm or below 2000rpm (for example if i take off hard and use full throttle through the gears the mixture stays rich). It is just in gear acceleration progressing from cruise to WOT that the problem occurs.
    Just to let you know the accelerator pump is working properly and the float level is right.
    The reason i'm asking about emulsion tubes is because i have tried many combinations of main jets and air correctors already with no improvement of the problem.
    Cheers,



    Dave


  9. #9
    1000+ Posts PeterT's Avatar
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    I've still got all that GTi injection gear if you're interested. That would solve the problem.

    '92 205 Mi16
    '90 Mi16x4

  10. #10
    1000+ Posts Dave's Avatar
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    Peter, i do have Tri 122 injection gear at home, but am still too poor to buy a fuel and ignition programmable computer. I dont see myself having the money to do it until i finish my degree at the end of the year
    Thanks again for your interest and help,
    On another note, how much power did you end up getting out of your 8Valve track car?

    Dave


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    Quote Originally Posted by Dave
    Peter, i do have Tri 122 injection gear at home, but am still too poor to buy a fuel and ignition programmable computer. I dont see myself having the money to do it until i finish my degree at the end of the year
    Thanks again for your interest and help,
    On another note, how much power did you end up getting out of your 8Valve track car?

    Dave
    First dyno run was a disastor. Base timing was out. So heading back tomorrow night.

    '92 205 Mi16
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  12. #12
    Fellow Frogger! AlsPug504's Avatar
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    Icon4 Leaness in mid range throttle

    "I dont think this problem occurs above 4000rpm or below 2000rpm (for example if i take off hard and use full throttle through the gears the mixture stays rich). It is just in gear acceleration progressing from cruise to WOT that the problem occurs."

    Ok Dave, that could well be that your float adjustment is to low! adjust it up 1/32 inch (about a millimetre) sometimes on high demand or when the vacuum increases across the carb as you describe the float bowl quantity may be starved.

    Al

    By the way check your float to make sure it has not just sunk!
    Last edited by AlsPug504; 2nd June 2004 at 10:19 PM.

  13. #13
    1000+ Posts Dave's Avatar
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    I am already running the float level a little higher than standard. Thanks for your input. Anyone else got any ideas?

    Is it likely that the problem is due to low vacuum as a result of my cam overlap?

    Dave


  14. #14
    Fellow Frogger! AlsPug504's Avatar
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    Quote Originally Posted by Dave
    I am already running the float level a little higher than standard. Thanks for your input. Anyone else got any ideas?

    Is it likely that the problem is due to low vacuum as a result of my cam overlap?

    Dave
    What is determining the leaness? Are you using an afr meter? if so wide or narrow band sensor? have you got A vac gauge? colortune? CO HC meter? and what sort of Afr metre display or data logging?

    And this is out of the blue! What plugs are you running how old?

    When Platnum plugs sh1t themselves mixtures can appear to make no difference.

    Has the cam be dialed in correctly?

    Your low vacuum problems are directly related to the quality of emulsion and vaporisation. So if the emulsion improves the mixtures may appear rich on a colortune and when corrected (lean to an Oxygen sensor) and the vacuum will increase only when the mixtures are backed off to the correct setting.
    This because when combustion efficientcy improves more oxygen becomes available so giving the oxy sensor apparent leaness.

    In fact, If it is rich on either side of 3000 and lean at 3000 then it could be that the emulsion either side of 3000 is really good. So if you lean of either side and richen or at least maintain the current mixtures in the middle that may resolve your drama.

    Just a thought!

    Al

  15. #15
    1000+ Posts Dave's Avatar
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    I am using an oxygen sensor and a a/f meter that reads from about 11:1 to 20:1a/f.
    The plugs are the 4 tipped items by bosch i cant remember what they're called.

    Dave


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    Budding Architect ???? pugrambo's Avatar
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    ok

    this is a bit of a backyard trick but i have seen mechanics do it and it does work

    set the car at idle at say 800-900rpm at operating temp

    grab a flat piece of steel or perspex but make sure it is flat and place it slowly over the top of the carby to pertially "choke" it

    watch for your revs to see if they change

    if it increases in speed then it is lean and if it decreases it is rich

    if the speed hardly changes or doesn't change at all with the plate almost covering the whole of the top of the carby then the mixture is close to right

    try this at idle then at 2000rpm and then higher if need be

    you may also be better off if you don't have one to grab a tacho so you can see any changes readily from in the engine bay

    if you try this let us know how you get on
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  17. #17
    1000+ Posts Dave's Avatar
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    Thanks for that mate, i'll give it a go when i have time and let you know how it goes. I have gone up to a 135 main jet in the primary throat and although i think its a little rich it accelerates a lot better and i have been able to re-advance the timing without making it ping badly. So i have gone from a 110 and 115 main jets (standard) in primary and secondary to 135 and 120. I need to find some 125 and 130 jets so i can test in between.



    Dave


  18. #18
    jaahn
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    Icon7 Carburettor emulsion tubes

    How is the carby rejetting going. Here is a new input from a new member. Having played with carbys in my(misspent) youth I thought I might put in my 2 cents worth as well !
    The problem that you have may be in the progression system. As has been pointed out there are several systems and finding the one to adjust is the trick. With a powerful engine (and also big carbs) the idle/progression provides fuel up to a surprisingly fast steady cruising speed. The idle/progression system has the expected mixture screw but also a jet, fuel well, air correction jet and sometimes an emulsion tube !! These may not all be removable or may only be drilled holes or passages, but they are there and do the job. I am not familiar with that carb so I am not sure, but the air jet may be a pressed in drilled brass plug set into the under side of the top. However its size may be reduced by putting copper wire or fuse wire up it with a loop at each side to hold it(works with jets too for trial) Temporary of course.
    I would suggest looking down the throat to see when the main discharge starts and see whether the problem is below or above this point. If below then reduce the progression air jet and/or increase idle jet. Note having the progression system working properly certainly improves fuel economy and drivability for normal driving in town??
    Cheers John

  19. #19
    1000+ Posts Dave's Avatar
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    Thanks for that John, I have just acquired some 125 and 130 main jets, so if i cant solve the problem with them i will look back to the progression system.


    Dave

    P.S Welcome to Aussie frogs, hope you enjoy it, a nice bunch of people we have here, check out the social calendar and try and meet some froggers in your area, and someone hook the man up with a sticker
    Last edited by Dave; 9th June 2004 at 12:26 AM.


  20. #20
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    Quote Originally Posted by Dave
    Thanks for that mate, i'll give it a go when i have time and let you know how it goes. I have gone up to a 135 main jet in the primary throat and although i think its a little rich it accelerates a lot better and i have been able to re-advance the timing without making it ping badly. So i have gone from a 110 and 115 main jets (standard) in primary and secondary to 135 and 120. I need to find some 125 and 130 jets so i can test in between.



    Dave
    Dave

    How did you go with the plate test ?

    have you tried it yet ?

    i actually use this method when setting the idle mixture on the current weber i have on the 604 till i get around to putting in the injected engine

    i normally blank off one side at a time to set the idle mixture on the other then do the other side

    makes it much easier to get both barrells the same then and i watch the revs on my tach meter (which on the 604 you have to double the reading )

    and would you believe the tach in the car reads high by around 200RPM
    3 x '78 604 SL

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    1 x secret project

    1 x '98 406 STDT troop carrier and i don't care if it stinks, i don't sniff it's arse Death by wank tank

    1 x '99 406SV 5spd wagon, time to burn more fuel

    1 x 1994 605 SV3.0


    WTD long range fuel tank for 605

  21. #21
    1000+ Posts Dave's Avatar
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    Hey Pugrambo i'm home today so i'm going to have a play around with it. I'm also going to plug a vacuum gauge onto the manifold aswell as before the carb to give us some insight into where we should install our water injection setups, i'll let you know how that goes.


    Dave


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