Emulsion Tubes are fragile, and very precise. Cleaning them is a little tricky, and gasahol is metered a little differently.

A gentle brass cleaning solution, that eats calcium and corrosion is needed?

Drilling out the tiny hole on the bottom has been recommended. A better idea of what size precise-drill-bit would be helpful.



I know to avoid using anything hard in the air-bleed holes on the tube, but maybe they need to be larger? What size? Are new holes needed? How high up the tube?

We have up to 15% ethanol in our gas, so a re-calibration is needed.

Maybe the air bleeds up top need enlargement?

In the picture below, there isn't enough detail on what is happening in the Main Fuel Well. The air-fuel mixing happens in that area, and is why it is called an "emulsion tube". It becomes a foamy mix at that point. As the level in the float-bowl changes, it affects the mixture. More on this would be appreciated.

What know ye, fellows of the kingdom?



Credits:
http://68vert.blogspot.com/2011/11/this-old-carb.html
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It is my opinion that nothing happens in the fuel well itself. Outside of storing fuel right there. Prolly why you couldn't find any other info on it. The emulsion tube Only turns the fuel well fluid in to small droplets of fuel to be passed on. You know how in real life blue + red = purple? So does it in your pic. Where the fine red fuel droplets meet the blue air from the air bleed they mix. Bigger holes in the emulsion tube will net bigger droplets of fuel. Drilling out the air bleeds will net more air atomizing with the fuel droplets. You can experiment with it for **its and giggles. But you can only go bigger. You can't go backwards. I'd leave it up to the carb engineers.

 

Yes, I wouldn't change a thing, until I really understood this. Just looking to clean up the holes properly...

Considering the use of copper wire and CLR.

 

Before getting off in the weeds with emulsion tubes, maybe you know this already, make sure the booster cluster itself is the right one for the carb you want to use. Lots of mix and match goes on with carburetor parts in 50 years. There is a letter code stamped on it, and the shop manual will list this, along with venturi size, jetting, power valve etc. I like the 2100 series, they are easy to work on. Once they are dialed in they seem to stay that way pretty good.

I don't know much about emulsion tubes other than sometimes they tend to crack, and folks have reported they can be brazed or soldered OK. I wouldn't mess with them unless you really have a clear understanding what you're trying to accomplish. A wideband O2 sensor really helped me dial the carb in.

Jetting is mostly cruise circuit afr mixture above say 30 mph or so but it has a big effect on the wide open throttle afr too. Consequently if the carb is jetted down for a good safe lean cruise ratio, it will be too (not safe) lean under load.

I talked to a carb tuner who seemed pretty knowledgeable, he didn't mention enlarging emulsion tubes, but the high speed (main) air bleeds iirc, the holes on top of the booster. I didn't bother enlarging those, only drilled out the power valve channel restrictors. Slightly. The guys that REALLY know this stuff can do some impressive tuning, especially for power. I was just trying to get some range out of a tank of juice. The widebands work really well for this. What you want is a pin vise, and numbered drill bits. Some of them are amazingly tiny, don't drop one or you won't be able to find it most likely. But without a wideband I don't think you'll have much way to know what's really going on. That, or a dyno.

 

I cleaned mine with copper wire, I still have a weird stumble. I wonder if its a little rich

 

Some of the racers will Swiss cheese the emulsion tubes in an attempt to deliver more fuel to the circuit. It does, but they are doing it to try to overcome restrictor plate limitations. As stated before, the booster assembly is a tuned assembly. If you want more through it, get one from a bigger carb like a 1.33. Or just get the whole larger carb. That way you can play with the jets to fine tune it. The two things that affect the tuning most severely for full run condition are fuel height and jets, and they are related. Fuel height sets the high side pressure on the jet, and the jet sets the differential pressure. Carbs can be quite a rabbit hole once you start getting into the science of them. Go to your local university library and do some research. Lots of good stuff, at least used to be, in the stacks back at NCSU. Burned up many an afternoon reading up on carbs, tubes and guitar pickups back in the day. Even found von Zepplin's lift equation. That was a different project...

 

You could use one of those tools that welders use to clean the tips of their torches.

 

Mix and match by a bulk carb rebuilder is a dang good point Ted. And what your carb tuner might have been thinking is a Holley rather than a 2100. The top air bleeds on one and no emulsion tubes. 4 or 5 years ago I was buying used Holley 600's of Evilbay, rebuilding them, and putting them back on evilbay. One time I made the mistake of saying I could custom tailor it via jets, P/V, plate, etc to "your engine". I didn't stipulate a V8 or I6. The buyer had a Mazda Rotary engine! After research on the net I found out the Rotary guys do this all the time. To make the Holley 600 work for them the air bleeds had to be drilled out to a certain dimension. That carb never came back. Never heard a complaint.

Sounds like Ted might have touched on your problem MPH. If you post the number off your cluster I'll check it out. And your carb tag number if it's still there.

 

The emulsion circuit will affect the A/F ratio in relation to the level of fuel in the main well. RPM and load affect the level of fuel in the bowl, which along with jetting and float height, affect the fuel level in the main we'll.

The emulsion action works not unlike slurping the last bit of soda at the bottom through a straw mixing air and liquid, as the level of fuel in the main well goes lower, more holes air exposed and more air is introduced.

So, the emulsion tubes affect the timing of the mixture delivery. I would suggest a wide band O2 gauge as has been suggested and mapping out your fuel curve under different conditions if you wanted to get serious.

 

Fanning the flame, I appreciate your comments.
Air-bleed enlargement comment is interesting. I would think a balance is needed between the other elements. Still not sure how the thing works exactly.

So, not really looking for tuning advice here, or not right now, anyway. I'm looking to understand a bit more on the functions. Especially how alcohol in the gas would change calibration, and perhaps some understanding on how altitude might be a factor. Just general balance issues and comparison to early '72 gasoline, really.

Thanks for paying attention to this particular situation, but generalized comments are welcome.

Gentle carburetor cleaners used so far. Last two cleanings only with Berryman's spray cleaner, and compressed air.
Obvious (Edit: buildup like crystals) visible in the holes now.
Calcium? Best cleaning solution? CLR or Simple Green ok? How long?

No extra attention paid to the little (.021" ???) holes in the emulsion tube so far. Never scrubbed, or poked-out. No cracks at last inspection. No modifications evident. No scratches. No cleaning at the pinched-end so far.

High-altitude use might warrant slightly larger air holes - debatable?
We have lower vacuum up here.

Wide-band O2 not in the immediate future. Agreed, that would be nice, but that goes in with future exhaust system. Long-range plan includes MegaSquirt and GM Throttle-body. Budget delayed by reality.

Ok if cruise is a bit on the lean side. (Big fresh radiator) Would prefer if high-load richness was delayed a bit, we use heavy throttle often given the low air pressure and hills. Already using a fresh 7.5 power-valve.

Details on drilling out Power-Valve (Econimizer) restrictions welcome, perhaps in a separate thread. Not sure if that is needed for high-altitude and gentle use.

Keep the knowledge flowing, especially how the flow works in the emulsion tube well.
There is a wealth of info found in Weber-carburetor data. Not sure what transfers to our 2100/2150s however.

Any guess on a rough RPM or vacuum reading where the Idle Circuit stops working? (Different by a dozen factors, I'm sure.)

 

A mechanic's vacuum gauge is your friend when it comes to engine and carburetor tuning. Plumb it into the cab so you can see what's going on at different speeds and load conditions. Every engine is going to be a little different, and that's before any carb modifications or upgrades, ignition timing, gearing, altitude etc come into play. The typical stock 6.5" or 7.5" PVs are a good place to start. I don't know why they didn't make them adjustable. But you can fine tune it a bit, if you want to get it a little more responsive, or tend towards a little more economy. The key thing is to determine your steady flat level cruise vacuum. Most stock or stockish engines are just fine with a 6.5" or 7.5" PV, but start running lumpy cams... and altitude plays a big role too. The point is making sure that thing isn't opening all the time or it will waste a LOT of fuel.

Hogging out PVCRs and high speed air bleeds, jetting can get a little complicated. I wouldn't attempt it without a wideband. Just a few thousandths makes a huge difference in the circuit so ya have to sneak up on it. It is true ethanol and modern fuels lean things out somewhat but it's also true carbs were also run pig rich. The important thing is to never go lean under load. But if you're at altitude you may not want to be hogging anything out on the emulsion tubes. That's the big problem as altitude increases as everything tends towards the rich side of AFR.

 

My theory on my weird stumble is that since I have 72 model lower compression pistons in my 69 390, it can't take the large cfm and fuel flow of my 1.23 C8TZ carb like it would if the compression was that of the 69 model. Anyone agree or disagree? It doesn't show any rich indication on any of the plugs. I have rebuilt my original carb and disassembled it again to make sure I didn't miss anything in the venture cluster. I even purchased a reman carb from "gottafish" on E-Bay and it does the same thing. This engine runs excellent other than this little pain in the %$^*.

 

With modern fuels, plug reading is about impossible. Not anything more than really rough generalizations. Those old charts with all the 25 different colored plugs don't apply anymore.

Should be able to get rid of a stumble. Smaller carbs tend towards better low end torque and crisp throttle response but it should work fine I'd think. Make sure ignition timing and curve, distributor is squared away. Then work on carburetor tuning, make sure no vacuum leaks, experiment accelerator pump shot size. Upon acceleration when the throttle plates just open, tends to cause a bog or hesitation stumble because air initially moves faster than fuel, so for an instant a little extra fuel needs to be introduced. That's what the accelerator pump does to smooth out the engine response. Too much of a good thing could cause a stumble too. It needs to be "just right".

On a 2100 there are a few different configurations of the pump rod, for different temperatures, holley's have different colored cams with different duration and a range of squirters available to tailor the pump squirt.

 

I have to echo the sentiment that these type proposed modifications are I'll advised, the suggestion of a wide band O2 sensor is a bare minimum and really itself isn't adequate to sufficiently hyper tune with. I'm happy to partake in the discussion and that it's been brought up as this is a fun enlightening topic, but I wanted to reiterate that to really know what's happening it takes precise equipment with track and dyno time.

That being said I wanted to add my general comment about air bleeds. It is the metered orifice through which air is drawn to emulsify the fuel but, it also sets the amount of air is "bled off", controlling the initiation of fuel flow as this determines the amount of vacuum required at the discharge nozzle to pull the emulsified mixture. A larger air bleed would require more vacuum and thus more RPM (because I'm talking about venturi vacuum, not manifold) to draw the mixture from the main well.

 

I'm painfully aware of all of this having been a mechanic for 35 plus years. This is not accel pump related, it is more of a low to mid range stumble such as used to happen in the 70's and 80's when EGR valves were first being introduced. Again, runs perfect other than this issue.