IDA emulsion tubes, How are they marked? Options

[Gary]

Hey 914-6 gurus,

Got the 914 last week after 5+ years of slumber at Aircooled racing. Picked her up in PA and trailered her back to Socal. First big storm chased me east, and coming back I beat the big storm of last week by about 5 days. Trying to dial in the carbs. Motor's a 2.7L built according to BA's book with MFI heads, E cams, RS P/C's. Have found the idles and mains too small (55 and 130). Going to order 60's and 155's. Air corrections are 180, which is correct. I pulled the emulsion tubes, but they aren't labled in any way I can tell. I want F3's. Can you guy help me with how to ID the size of my e-tubes?

Oh, I know, pictures - they'll be coming once she's roadworthy. Need to bleed the brakes and get the lights all working. Last update was here: Gary's car.

[TimT]

Emulsion tubes are marked, but the marks are usually very hard to see. With my eyes iI need a magnifying glass to be able to make out the markings.

[ArtechnikA]

QUOTE (Gary @ Dec 10 2005, 04:59 PM)

I want F3's. Can you guy help me with how to ID the size of my e-tubes?

emulsion tubes are not identified by size, but (approximately) how they perform in the transition region. the size, number, and location of the little holes is as much a black art as anything.

i daresay most triple-choke Webers have F26's. look for teeny numbers around the rim or on the tube itself.

if you really want F3's, they can be had through PMO; i just got a set there...

i presume these are 40's. i donno if the 46's are different, but if you wind up ordering a set, it'd probably be best to mention which you've got.

[Carl]

In the photo below, the left tube is an F26, the right is an F3. You can see the stampings on the lower part of the tubes.

C

[bd1308]

holy cow..

are those dimples the individual paper towel texture things?

Emulsion tubes at 1000x magnification....

(IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

b

[Carl]

Well, I keep getting all this email about how to make my emulsion tube bigger. Must've been the enlargement cream ...

[campbellcj]

Sorry for the mini-hijack but I currently have F26's as well and am wondering if switching to F3's might help smooth out the midrange? Mine is a 2.2S-spec and IIRC the 2.0S carbed engines typically used the F3's, but I didn't set up these carbs originally and am unsure if the F26's were deliberately chosen or just "happened". In other words, what is the functional difference between these emulsion tubes?

[bd1308]

QUOTE (Carl @ Dec 10 2005, 03:49 PM)

Well, I keep getting all this email about how to make my emulsion tube bigger. Must've been the enlargement cream ...

(IMG:http://www.914world.com/bbs2/html/emoticons/av-943.gif)

b

[Gary]

QUOTE (Carl @ Dec 10 2005, 01:29 PM)

In the photo below, the left tube is an F26, the right is an F3. You can see the stampings on the lower part of the tubes. C

Thanks guys. I pulled all 6 of mine and they're not stamped anywhere.

Carl,

thnx much. Mine resemble the F3s in your photo. Obviously, if there are other e-tubes with the same hole configuration but different hole sizes, I won't be able to tell very well.

[Carl]

QUOTE (campbellcj @ Dec 10 2005, 02:06 PM)

Sorry for the mini-hijack but I currently have F26's as well and am wondering if switching to F3's might help smooth out the midrange? Mine is a 2.2S-spec and IIRC the 2.0S carbed engines typically used the F3's, but I didn't set up these carbs originally and am unsure if the F26's were deliberately chosen or just "happened". In other words, what is the functional difference between these emulsion tubes?

My understanding is the same and Rich's. Emulsion tube design was a trial and error process and the number means nothing except to identify the tube in the process of experimentation.

Reading I've done indicates that F3, F11 and F26 are the most common E-tubes in 914/6's, at least in the 2 litre cars. I don't know which tubes were used in the larger carbed engines. There are surely experts in the club that know about this.

The function of the tubes is to slow the gas delivery by mixing air into the gas flow as engine speed increases. Simply using the increased airflow to draw more gas into the airstream results in rich mixtures. Weber addressed the problem by using the E-tubes to slow the increase in gas flow by bleeding air into the stream. The placement and size of the holes does tie to mid and high speed performance and engine smoothness.

I once found an article about this on a VW web site (below) that was very good even though the examples don't apply to 914's.

[Carl]

Sorry for the little-bitty type. I'll try to fix that.

[J P Stein]

The E-tubes aerate the fuel from the main jet. This helps the gas to atmoize when it hits the air stream in the aux venturi. More aeration will also lean out the mixture, bigger bubbles-smaller bubbles are a function of the size of the holes drilled in the tubes, more bubbles/less by the number of holes....location of the effin holes prolly makes a difference also but I'll be damned iff'n I can figurer that one out. all of this works in conjunction with the air jet which supplies the amount of air available for the E-tube to play with.....it's enuff to make a grown man weep trying to figure out what is best. (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)

I went with B Anderson's whole carb set-up for his hot rod 2.7L (along with 60 idle jets).....KISS. Close enuff, I figure.


Chris:
Were it me, I'd look elsewhere for a solution.....got a dyno? (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[Carl]

From VW Resto-Custom website, 2/4/2004:

There are some basics to consider when looking to change the emulsion tubes. What you first need to consider, is "why" you would like to change them. When I began educating myself on emulsion tubes, I had exhausted ALL other tuning practices to achieve a smooth, proper acceleration curve from my carburetors.

Having said that, I will assume you are familiar with the idle jet, its circuitry, and what part of acceleration it is responsible for. Secondly, I'll assume you are familiar with the main jet, its circuitry, and the role it plays, when "taking over", as the idle circuitry's contribution diminishes, as the throttle plates open wider.

The reason the above two sections are important, is that the emulsion tube plays a big part in the transition from idle to main circuitry. Put plainly, the emulsion tube plays three very important rolls: 1)It contributes to the "timing" at which the main circuit begins to "come on", 2)It emulsifies, or mixes air into the liquid fuel, and 3)It compensates for the difference in density of fuel and air, as air flow increases (high RPM, say above 5500 RPM). For the third one, because liquid is more dense than air, a fuel mixture would increasingly become more rich, as air speed increased. This is not what we want.
Think of an emulsion tube as a straw with holes it in. If you try to drink out of this straw, and the holes in the straw are above the surface of the liquid, you will not get as much fluid up the straw. Instead, you will get a mixture of air and liquid. If you raise the level of the liquid, thereby covering up some of the holes in the straw, you will get more "liquid" than air. You would get the same effect, if you were to lower the holes in the straw, thereby, having them covered with the liquid, as opposed to them being "in the air".

This first analogy can describe one of the obvious physical differences of one emulsion tube to the next. If you place your F9 emulsion tube next to another (I do not recall what other emulsion tube you had, F2, F7, F11 ??), you can easily compare the number of holes, as well as the placement of holes in each tube. In general, if the number of holes are the same, the location of the holes (as measured from the bottom of the emulsion tube, up) can allow you to easily identify which one would allow the main circuit to "come on" sooner. The emulsion tube with lower holes, has the same effect as the straw example above. The main discharge nozzle, when "sucking" from the emulsion tube well, will get more fuel quicker, if the holes in the emulsion tube are lower, and in fact, "covered up" with fuel. This means the holes are below the fuel level, as set by the floats of the carburetor. In a situation where there is a flat spot, when driving, due to a lean condition between the idle and main circuitry, an emulsion tube with "lower" holes, will help the main circuit "come on" sooner.
Another characteristic of the emulsion tube is the outer diameter (OD) of the emulsion tube body, and "where" it might be larger (a step). The emulsion tube, when installed in the carburetor, resides in what as known as the emulsion tube "well". This "well" has a fixed diameter that accommodates the emulsion (and associated jets). The fuel level of the emulsion tube is equal to that of the main carburetor bowl, when AT IDLE. However, as the air speed increases, and the effect of fuel being "sucked" from this well, as well as incoming air "pressure" through the air corrector jet, the level within the emulsion tube well will fall, exposing more holes in the emulsion tube to air. This is how the emulsion tube, and its series of holes leans out the mixture, as air speed increase. Where the OD of the emulsion tube comes into play, is the amount of fuel it displaces with the well it sits in. A large OD emulsion tube will leave very little room for fuel.

Because the amount of fuel is less, because of the "fat" OD'd emulsion tube, the overall fuel level will fall quicker, as the main discharge nozzle "sucks" it out. This will make this "fatter" emulsion tube have a "leaning" effect quicker than one that is smaller (skinnier). A smaller diameter emulsion tube will displace less fuel, and allow a greater quantity of fuel in the emulsion tube well. This will take "longer" and more air speed to drop the level of fuel in the well.

This will make more sense, if you get a cross section diagram of a carburetor (IDF, IDA, or most any Weber). You'll see that the float level, as it maintains the fuel level in the bowl, also sets the idle fuel level in the emulsion tube well. Because the emulsion tube well is so much smaller by comparison to the bowl, its fuel level will drop dramatically quicker than the main bowl. Proper fuel pressure is required to make sure the bowl can try to maintain a constant fuel level, to properly supply fuel to the emulsion tube well.

In summary, I first recommend that you identify "why" you feel you need to change emulsion tubes. Reasons could be things like: 1)A flat spot in between idle and main circuitry, 2)A need to enrichen, or lean the mid-range, to upper end fuel mixture. Although not the only possible reasons to change, these are what the emulsion tube helps to control. In both cases, you would need to know your air/fuel mixture strength. This is best accommodated with an air/fuel meter, and of course, an 02 sensor in the exhaust.

As an example, I had a flat spot at about 1700 - 2000 RPMS. This is the point at which the idle jets start to fade, and the main jets begin to take over. With my 02 sensor, the air fuel gauge read "rich" at this RPM range. This meant either the idle jets were too big, or the main circuitry was coming on too soon. The over rich condition was caused by both the idle and main circuits contributing fuel to the engine at the same time. My first order of troubleshooting was to try smaller idle jets. This helped the over rich condition at the above specified RPM range, but caused stumbling, and flat spots at lower RPMS (lean condition just off of idle, and up to 1700 RPMS). Since this wasn't the solution, I put the original idle jets back in, and looked at my other option: slow the mains down; not let them come on as soon as they were. To do this meant I could have tried a smaller main jet. But, my 02 sensor told me that my fuel mixture beyond 2000 RPMS was correct. I simply needed a slight delay in the time in which the mains came on; hence a change in emulsion tubes.

My IDF's came with F11 emulsion tubes. I ended up using F15's. The F15ts were nearly identical, with the exception of 8little holes about midway down the emulsion tube. On the F15, these 8 holes were about .030" higher than the F11's. This made the main discharge nozzle "suck" a little harder before actually getting fuel. As a result, the F15 slowed the mains from coming on. This allowed the idle jet and its circuitry to do its job, up to the point where the mains would come on, without excessive overlap, and an over rich condition.

Below is a diagram of both an F11, commonly found in IDF 44's and the F7. The F7 has been known to help with the idle/progression circuit (or lack of) in the IDA. It is easy to see the difference in number of holes and their placement in addition to the diameter differences, and placement of the step. In diagnosing my overly rich problem (described above), it was recommended that I try the F7 emulsion tubes. I was very skeptical, as it seemed to me that this would make my problem worse. I tried them anyway, which did prove to be an incorrect solution. With the holes lower and fewer on the F7's, the mains actually came on sooner; just the opposite of what I needed.

[campbellcj]

FYI - PMO has just acquired a small shipment of F3 tubes after thinking they were going to be NLA. Super nice people to work with, too. (But maybe someday they will get email... (IMG:http://www.914world.com/bbs2/html/emoticons/rolleyes.gif) )

[brant]

good to know.
thanks
brant

[Downunderman]

Here's a chart that might be helpful.

[brant]

Just for reference...
we thought the IDA and IDS e-tubes would all be the same.
we bought after extensive searching, a set of F33's because this exact chard indicated they were worth trying..

F33's do not fit into IDS 3barrel carbs.
hopefully no one else will make this mistake that I made.

brant