RANT!
I was going to post this in one of the already existing IDA threads that I have post whored to death, but i figured I'd start a new discussion to amke it easier to search and since this applies to all weber tuners.

Emulsion tube, so what the hell does it do? The easy answer is that it mixes air with fuel as it enters the aux venturi and is sucked into the engine. But, that's not all it does. Actually that's the smallest part of what the tube is actually doing. The e-tube is actually a fuel brake. It slows the progression of the fuel metered by the main jet. Without the e-tube the car would continue to run richer and richer as the revs rise. See as the air speed increases and pressure drops across the chokes, vacuum in the float bowl increases two fold, so there has to be a way to meter the fuel down to use able amounts. The emulsion tube does this two ways. The first is by the width of the tube. The wider the tube is the tighter it fits against the main circut galley, therefore the less fuel it allows by and the leaner the mixture. The second way it slows the fuel's progression is with the air corrector jet and the holes in the tube. The emulsion has different series of holes along the length of the tube. The higher the holes the LOWER the RPM range effected. When the etube assembly is in the carb it is half sitting in fuel, half not. The depth of the fuel in the main circut is controled by the float setting in the carb. You see the higher the fuel level is in the etube galley the sooner the main circut will come on. Also, the less amount of holes above the fuel the sooner the main circut will come on. Air and fuel will take the easiest path to get to the vaccume created in the engine. If it's easier for air to rush past the ac jet and through the e-tube and into the carb than it is for the fuel to be pulled out of the float bowl that's exactly what is going to happen and that's why the main circut is comming on late.

Now all of us rotards using webers have experianced the annoying 3000 rpm cruise stumble. Now we all under stand that the cause for the stumble is a lean spot fron the progression fron the idle circut onto the main circut. So how do we fix this? First by extending the idle circuts amount of time functioning to supply enough fule to run smoothly past 3000 rpm when the main circut starts to come on. So by richining up the idle circut we can over come the stumble. This how ever has it's draw backs. Rich idle causing terrible gas mileage, strong petrol smell, fouled plugs, as well as a rich sluggish bottom end. With my 48IDA small street ported 13B my car runs best on the idle circut with a 65 idle jet and a 100 a/c, but once the main circut approaches it can't supply enough fuel to over come the hump, so my solution was to run bigger idle jets to get over the hump, but that comes with the disadvantages I mentioned before.

The other option is to somehow cause the main circut to come on earlier. There are two ways to make the main circut come on earlier. As I mentioned before the first way is by controling the fuel level inside the main circut galley you will control how soon the main circut begins. So how do we raist that level and how much can we raise it before we have problems? The answer is not much. With a weber IDA you have to set the float to between 5.5-6mm. .5mm of varience to work with ("0.0019 incase you don't understand metric.) anything more than that and you'll flood the car anything less and it'll run grossly lean. Now you see how important float level is don't you. The second way is by metering how much brake that etube is putting on the fuel.

First a thinner etube will allow more fuel to pass by. 2nd a smaller air corrector jet will allow less air through the etube braking the fuel less; and third by getting an e-tube with less holes in it or holes in different places will allow more fuel into the aux venturi.

Now most of us have been using the F-11 and F-16 e-tubes and it always confused me as to why our cars required such small air correctors until I learned what the e-tube was doing. I thought it was just a rotary thing to run 205 mains with 120 a/c like I am, but when I go to my local shop and the 400 BB cobra guys are running 130 mains with 175 a/c's. The probelm is that we're using the wrong e-tube and trying to fix that issue with restricting the air to it by using teeny tiny air correctors.

So, I've been on the hunt for the last 3-4 months trying to find some sort of guide for e-tubes or list some where. I haven't come across much but this stuff.

This is an f-14 tube. it's exactly what we don't want. it has holes in the top causing a late start and leaning out the bottom end and none in bottom giving a very fat top end.

this is a f-19 with holes all over it like an f-11 causing a late start and lean every where. Exactly what we don't want. I have a chart in a Weber book that I have plus this hand written chart I found online.

So far my best guess is that f-7's are going to be much better than the f-11's or f-16's everyone recomends. Hell even I recomended f-11's in the past.
I ran them in my turbo FB for about a week before it spun a bearing. and in that week it drove about a million times better. I don't know what tube is going to be the answer yet, but I think I'll find it soon enough.

Remember if you go out and start buying e-tubes you have to buy new main jets and air correctors too because it's a harmony of all three parts to make it work right.

 

Now, my Weber setup was far from perfect as you know. When I tried the F7 e-tube, it caused an overly rich low-end, even with 40F9 idle jets. However, if I remember correctly, it did largely eliminate the stumble. Reading this makes me wish I'd experimented with the F7 more.

 

I bet you didn't change your main jet or air corrector did you. Just my guess but i figure with a f7 in my car ill use a 180 main and 170 corrector. I just ordered f7 and f8 tubes to try out. Remember that an f7 is going to start the main circut earlier and on the top end it will flow much more fuel than a f11 so you can run a smaller main to make up for the difference in added fuel flow.

what do you mean was? Are you going with injection? If so I'll buy all your jets.

 

Did the F7 go in the carb that also got the brass floats?

 

Excellent explanation. I have a RB prepped Dellorto and on of the mods is a bunch of holes drilled in the emulsion tubes. I suspect for this very reason. For the Dell its a #8 emulsion tube with a bunch of holes drilled by RB. This is the first time I've seen a solid explanation that accounts for why they may have done this.

This thread will need to be archived when its played out. Good info so far.

 

The thing was, that's exactly what I had. 40F9 idle jets, F7 e-tubes, 180 mains, and 170 air correctors. Maybe a smaller main would have been better for me. Like I said, I didn't really experiment with it much. But, it eliminated the stumble, so it could be what we're looking for.

Nope, I'm not going EFI in my FB. At least not for now.

Jeff: Yes. Too bad, isn't it?

 

Maybe we can come up with a port size that will match the F11, then.

 

lol smaller than stock ports the f11 is just too lean for the rotary.

 

F16 does richen up the bottom end, I end up running a main fuel jet that is .05mm smaller than what I ran with F11. And F16 does have a strong midrange too.

But I'm open to using the F7 if it's a better all around package.

 

The carb was used on an engine with very large streetports and was actually pretty good all around. Percent was saying it might work better on a 12A or a non ported 13B. I don't know either way since I haven't learned how to tune webers yet. I'm just going by what he and others was saying. All I know is how it ran on the ported engine, which was pretty well for the most part.

I'm thinking slightly smaller ports on a 13B and a slightly heavier flywheel will improve the driveability for daily driving applications. This is what I intend to do with the carb. Heck it already served daily driver status in Percent's car. Why not try it again?

 

So it's essentially a vacuum break?

& does this mean the Weber does not have a transition circuit like the Nikki's?

 

interesting thread!

mines nice cause i can cheat, 12a PP, i just bought the jets and stuff in the competition book.

em tube is an F8

its not running yet, but it does smell like gas already....

 

That's interesting that it richened it up since from my understanding the tube is much leaner tube than the f11 due to the 8 holes above the fuel float line.

 

f7, f8, and f16's shipped and on the way results to follow.

 

NOICE work MAN!

 

Also there are two "families" of e-tubes. The first of which has the holes drilled in them perpendicular to the tube body. Like the ones shown above. Now if you look at the bottom of the tubes in the pictures above you can see that where the fuel enters the galley its comes out at an upward angle of aproximatly 45* to help facilitate fuel flow into the galley. There are e-tubes that also have the air holes drilled at the same 45* angle to lessen the restriction of the air emulsifiyng with the fuel in the galley. So, they're kind of counter acting the effects of the holes themselves making the air correction brake slightly less. The f-11 and f-16 are both supposed to be drilled this way.

I guess you can see how confusing this all is. Weber tuning isn't a "black art" as many have stated. Now the e-tube design sure is considering there are 4 things that effect how everything works. Size, amount of holes, placement of holes, and angle of holes, but once you get the right tube the rest is cake. And as anyone who's ever taken a physics class knows, a properly tuned and sized carb setup will allways make more peak HP then FI.

 

Nice write up. Emulsion tubes are so damn tricky cause the numbers don't really mean anything. I have had really good results using F20s. I have no stumble at cruising speeds. Next summer I will be running a wideband so I can finally see how well my carb is tuned.

I have tried a pair of F7s and seemed to run really rich. Didn't really play with them that much though

 

I've never even heard of F20's. Please post pictures of them.

 

I will pull them tonight

 

The F16 is a special gem that has the holes angled upward, helping instead of retarding fuel flow. It richens the bottom end and causes the mains to come online earlier. The F4 to F15 family of etubes have their holes drilled at a 90* angle to it's axis which retards flow since the fuel is trying to flow upward to the aux venturi.

The F16 midrange is leaner than the F11's but not considered too lean. F16's really do have more power in the midrange. The last Hangover Run I went on we were buzzing along the 110 freeway and some 2nd gens were impressed the repu could keep up.

This book helps explain it more, and has measurements of etubes too:
http://books.google.com/books?id=OSL...esult#PPA37,M1

 

I have that book, and it is wrong. I have owned F-11's that were both drilled straight and at angles. I, nor has the local shop I deal with, has ever seen a F16 that has been drilled at an angle. If your's are, maybe there was a change in production. As I said before I have used F-11's that were drilled both ways. The general consensious was that F16 was a typo. Also in the chart he has listed he has incorrect measurements and hole anounts on the F-11 and at least 2 other tubes on that chart. FYI.

 

Here is a picture of the F20. I cannot for the life of me get a good clear pic of the tube, sorry guys. I drew the pic next to it to help show where the holes are.

The holes where is gets thicker are drilled at an angle. Let me know if I can answer any questions.

 

Thanks for the pix. I'll post pictures of my 7 8 11 & 16 when they get here.

woot my 5000th post! I officially have no life.

 

I found these while I was board at work this morning. Pretty nice diagrams of various tubes.

 

OMG you kick ***. where did you find those?