Lets talk Emulsion tubes

[priobe]

Ok,

Lets talk emulsion tubes. I rather not discuss what the Weber books say regarding the Etubes, but rather discuss real world experience.

The books say not to change the etube unless on a dyno or have a very good feel for the way the car drives. I think those of us that have change these tubes know different.



When looking at this chart it says it goes from richer to leaner. It also indicates that the F7 is a richer tube than the rest.

What is kind of confusing (at least for me) is it say rich low. What is low RPM or vaccum?

[priobe]

Anyone wanna talk E-Tubes?

[priobe]

Ok, Let me start.

Wouldn't it make more sense to create groups for these emulsion tubes that are the same size diameter and then concentrate on the positioning of the holes.

For instance, Etubes F8, F7, F2, F3 can be 1 group. (7.5 diameter)
F11, F15 (8 diameter)
F9, F16, F14, F19 in another group (8.2 diameter)

Now lets take alook at the 1 st group.

Although f8, and f7 look the same in the drawing, I am sure they are different. But I am not sure how they are different without conculting the book. However, it seem like the tubes with the holes on top will begin to lean out the mixture as the RPM begin to climb starting from 2500 +.

If you begin to move the holes on the emulsion tube further down, it will delay the mix from happening resulting in a richer mixture during the transition phase at lower RPM.


Now, the reason why I am mention to group the Etube by diameter is so the Etubes will have the potential to flow the same amount of fuel until the holes are exposed, which is caused by the fuel level diplacing from the engine as the rpm increasing.

The way the chart is displayed does not recommend an accurate suggested rich to lean solution.

FYI the small the diameter of the tube the leaner the mixture

[priobe]

does anyone know anything about etubes that they would wanna share?

[DMXF]

You forgot to include F5 on the list. That tube is supposedly ideal for some Cobra configurations.

[Rick Parker]

Phil: The emusion tube effect how the A/F ratio is monitored at part throttle. With foot to the floor it's not doing much. What are you attempting to achieve?

[priobe]

Rick,

I agree with you. However, I dont recall seeing a chart of Etubes that list from rich to lean in a proper order.

Also, the etubes have a reasonable amount of influence on driveablility. (cough cough) more so than the idle circuit.

My ultimate goal is to have a section (maybe here) that one can follow based on symptoms one is experiencing that they can intelligently purchase or recommend a etube.

These Etubes are expensive and to purchase them and make a mistake surly hurts the pocket.
I think now alot of people are doing the Monkey see Monkey doo mantality and not taking into account altitude, final gearing and so forth.

[Gaz64]

One of my Weber books lists these emulsion tubes versus cylinder capacity:

F11 - 250cc to 325cc
F15 - 275cc to 400cc
F16 - 350cc to 475cc
F2 - 450cc to 575cc
F8 - 550cc to 675cc
F7 - 675cc and above

[priobe]

Gaz64,

Have you tried using this chart for your setup?

I dont believe this will adapt to my configuration. I think the idle circuit and the mains have something to do with which tube to use.

Now does the fuel flow from with in the tube or from the outter well of the tube.

Also, the higher the holes on the tube, does this mean that you will have a leaner mixture at the lower portion of the RPM when the Etube starts to function?

[priobe]

ok looking at the Weber book regarding Etubes

Why did they group (F1, F2, F3, F5, F9, F11, & F15) to be on the same tube diagram but when you look at the other like F14 and F16 which are the same except the holes on the F14 are high they decided to use a different picture?

[priobe]

Forget it, I see that the step is different.

[carmine]

In my own personal opinion.
Anything to confuse the issue of choise is what is usually published when it comes to weber secrets.
In turn they make a ton on jetting and e-tube sales.

[Gaz64]

Originally Posted by priobe

Gaz64,

Have you tried using this chart for your setup?

I dont believe this will adapt to my configuration. I think the idle circuit and the mains have something to do with which tube to use.

Now does the fuel flow from with in the tube or from the outter well of the tube.

Also, the higher the holes on the tube, does this mean that you will have a leaner mixture at the lower portion of the RPM when the Etube starts to function?

I run an F2 in my V8 and an F15 in my little Datsun.

My understanding is the main well has liquid fuel in it prior to main system startup,
the inside of the emulsion tube to just below the lowest holes will have liquid fuel from this lowest point up to the float level.

The volume in the well is dictated by the outside and inside diameters of the tube.
Thick tube high holes - lean; thin tube low holes only - rich.

At the onset of main system startup, dictated by choke size versus cylinder displacement versus air corrector diameter, the bleed air admitted to the inside of the tube blasts through the fluid and to the auxilary nozzle to satisfy the negative depression created by the induction stroke.

As the engine speed increases the fluid level drops exposing each row of holes and leaning the mixture.
A fixed choke carburetor needs a form of correction to keep the A/F ratio consistent across the useable rpm band.

The A/F ratio would go from say 14:1 to "who knows" how rich without an emulsion tube/air corrector prior to the nozzle.

High holes would be leaner at startup, low holes only would be rich.

As stated from "How to build and power tune Weber and Dellorto DCOE & DHLA Carburetors:

"The following shows the Weber listing going rich to lean or large cylinder capacity to small cylinder capacity:
F7, F8, F2, F11, F16, F15, F9"

Of course they are many other tubes out there and some others including members here have experimented modifying existing tubes to their liking.

It's all about getting the engine cleanly onto the main system with the minimum amount of extra fuel from the accelerator pump.

[priobe]

Originally Posted by Gaz64

It's all about getting the engine cleanly onto the main system with the minimum amount of extra fuel from the accelerator pump.

Ok,

I agree and understand you thus far. However, then why are so many people mentioning that they are running 00 exhaust valves when they should be running something with value i.e. 50.

In regards to the emulsion tube being related to the cylinder capacity, I think the Etubes are related to the camshaft to a certain extent. Of course the cylinder does play some value but I think the camshaft is more closely related.

Cylinder capacity will dictate the volume of air but the camshaft will control the air flow and time / RPM.

I am running a .680 lift camshaft and the Webers hide this very well. Transition is smooth and I plane out to the main at a Max 12.5 A/R

Also I have noticed that when your transition circuit is not correct, you will experience poor acceleration off of corners.

In addition, upon decelleration, I am get little to no backfire simply by changing the tubes to achieve a proper transition; not the mixture screws.

Also regarding the chart. It seems that the chart that is posted on CC is incorrect according to your chart. The chart posted above indicates F8 is richer than F7, and your chart shows F2 is richer than F11.

This is why I suggest that all alike tube diameters should be is 1 family (say 7.5)then a 2 nd family (8.0) and so forth. After grouping these tubes alike is diameter size then we can look at the orientation of the holes to decide rich or lean. By mixing the tubes with diameter size you really can not tell if you are going rich or lean because there are too many variables.

Any thoughts?

[Rick Parker]

One thing that I realized had not been openly discussed was the elevation that we individually live at, it certainly has some distinct effect on what variables are applied to our particular application.

I would agree with Gaz64; thel least amount of fuel injected by the accelerator pumps the better. If the E-tubes are lean in transition and cause a stumble, the most common Band Aid is to dump fuel with the acclerator pump circuit in an effort to rid yourself of the carb sneezing.

If you are using carbs that are not "New" the fitament of the Aux venturis in the Carb body must be checked. It is imperative that there be a tight fit to effect a seal in the fuel passage from the Main Well to the Aux Venturi, if you can gently wiggle the venturi there will be a leak that will cause all sorts of transition problems, check it on each carb. Sometimes the small spring clip on the venturi becomes loose and does not exert sufficient force to keep a tight seal, there is a fix for this and it should be considered.

[priobe]

Rick,
I agree with the elevation issue. Here in FL. our land is flat and at sea level. This is something I was never able to experience. However, during my readings on carbs, for what it is worth, they say you can get away with not jetting a carb up to 5000 ft above sea level. Now I have not idea if that is true.

If anyone can add to this it would sure be helpful.

[DMXF]

Priobe - You should be able to model the etubes to establish a good matrix as to exactly what each would accomplish. It would no doubt be quite involved and should ideally include correlations to various testing, as available (this aspect may be very important). You can calculate hole areas, passage areas, correct for some holes being at an angle, etc. You may end up with something that can be used to determine the tube number direction to go, or even maybe how to modify an existing tube by drilling more holes, etc.

[Gaz64]

It does seem the more reading one does, the more confusing it becomes as well.

The above listing shows F8 richer than F7 yet the hole placement is contradictory to this.

F2 would be richer than F11 because it's smaller in diameter.

Agree with grouping them via diameter first, then step placement, then hole placement.

But then you end with a lot of groups, it still may help to list them correctly from rich to lean.

And the yes the camshaft does have a greater influence on airflow, I guess it's the combination of capacity, compression and camshaft.

[priobe]

Well,

I think once you break them down into the 3 groups, you can pretty much pick any tube from any group to get a feel for which group of tubes you will need to stay within.

Once you ave figured this out then you can make a determination whether to go rich or lean in that group.

If you decide to change the choke to a larger or smaller choke, you should still stay with your grouping to to not complicate the matter. (I have not tried this experient yet).


On another note: What is the recommended choke to be used on the 390, 427, + engines.

I have herd that the 48 mm are too small for the BB motors. However by looking at a chart it looks like 42 - 44 mm choke should be just right. If it is a street car or road race side on the small part of the choke selection.


Also, if you run these 52 mm carb bodies what difference will make if you put the 40 mm choke back in it.

Aren't you just restricting the carbs right back down to the size of the choke?

And why not remove the choke all together on the 48 mm bodies, the horns will correct the intial entry of the air flow.


Just questions I have?

[DMXF]

Probably just wasting my time posting it, but here goes:



You can back calculate the choke size by picking an appropriate point on the line and then rearrange the equation (plugging in your displacement).