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Old 12-15-2011, 10:03 PM   #1
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Default Carburetor guys...let's have a discussion on emulsions.

And their effect on the fuel curve. This is something that's always been sort of a voodoo to me on a carburetor....along with throttle slot restriction sizes and power valve channel restriction sizes. I'm anxious to learn some more about all of it!
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Old 12-15-2011, 10:08 PM   #2
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Default Re: Carburetor guys...let's have a discussion on emulsions.

Also, let's discuss possible tuning differences between a street/strip footbraked car, and an all out transbraked race car.
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Old 12-16-2011, 01:17 AM   #3
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Default Re: Carburetor guys...let's have a discussion on emulsions.

Subscribing. I'm interested in hearing this stuff too...
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Old 12-16-2011, 07:14 AM   #4
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Default Re: Carburetor guys...let's have a discussion on emulsions.

Subscribing here. Just hope this thread stays with the theme and doesn't become another bashfest! Alot to be learned on the subject, great idea for a thread!
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Old 12-16-2011, 07:22 AM   #5
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Default Re: Carburetor guys...let's have a discussion on emulsions.

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Subscribing here. Just hope this thread stays with the theme and doesn't become another bashfest! Alot to be learned on the subject, great idea for a thread!
Amen. I'm hoping Jmark, Carbguy, and Contraro Dave jump in here sometime today.
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Old 12-16-2011, 07:58 AM   #6
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Default Re: Carburetor guys...let's have a discussion on emulsions.

If you really want to learn about emulsion, the best thing you could do is to go to motorsports village, click on fuel systems, open the emulsion thread, and read the entire thing. Pay close attention to shrinker. It's ridiculous how intelligent that guy is. You'll learn about 8 times more than you even want to know. I think mark would agree.
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Old 12-16-2011, 09:45 AM   #7
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Default Re: Carburetor guys...let's have a discussion on emulsions.

I'll give you the long version first, complements of Tuner. Copied from the Innovate Forum, the rest of the thread is worth looking over as well. Once you read it a dozen times or so maybe I can simplify it a little. Still miss my chats with him.


Quote:
Tuner wrote:
Why didn't you ask a simple question?

In the thread “750 Holley carb help” Klaus made this statement, “On carbs it's very important that the correct two-phase flow gets established during emulsion. Otherwise you will see RPM dependency of AFR.” Thank you Klaus, but forgive me if I see your remark as a profound understatement. Incorrect two-phase flow is at the root of all this aggravation. People who have drill bits but don’t know why to use them have been molesting innocent carburetors for a long time. Now some of them are in charge of the manufacture of new carbs and they think they have improved them by using larger drill bits to make the air bleed and “emulsion” orifices. I guess the guys that engineered the original carburetors on the old muscle cars were pretty stupid or they would have “improved the emulsion” 40 or 50 years ago when they had their chance. After all, they had the awesome power of the single-point ignition system at their disposal, they shouldn’t have been afraid of a little soot.

It is well documented that introducing air into the main well encourages low signal flow and can encourage or discourage high signal flow. The natural characteristic of a plain jet and nozzle (no air) is to get richer as airflow increases. The purpose of the air bleed system is to modify that behavior to accomplish a constant (or the desired) air/fuel ratio over as wide a range of airflows as possible. The particular ratios for power and cruise are realized by the selection of jet and rod or jet and auxiliary jet (power valve channel). The purpose of air bleeds is not to emulsify but to accomplish the correct fuel delivery. Emulsion is just a beneficial side effect.

What I’m going on about here is Klaus’ remark about “correct two-phase flow”. That is the description of a fluid flow that is made up of a liquid and a gas flowing together in the same conduit. As the ratio of gas to liquid increases (more gas, less liquid), at some point the gas bubbles coalesce from many small ones into a few big ones and the flow starts to “slug” and become erratic. The carburetor nozzle spits like a garden hose with air in it when there is too much “emulsion” air.


An emulsion of air and fuel has reduced density, surface tension and viscosity compared to fuel alone. This increases the flow of fuel considerably, particularly in low-pressure difference operation, at low throttle openings or lower engine speeds. Just how much of an increase (richer) is dependant upon where and how much air is introduced into the fuel flow.

Mainly, what must be understood is that because the fuel discharge nozzle connects the venturi to the main well, whatever the low pressure (vacuum) is in the venturi, it is also the pressure in the main well. The air bleed is in the carb air horn or somewhere else where it is exposed to essentially atmospheric pressure, which is higher than the venturi pressure. This pressure difference causes air from the air bleed to flow through the emulsion system into the main well and to the nozzle. The flow of air can have very high velocities, approaching sonic in some orifices. The airflow literally blows the fuel toward and through the nozzle. A larger main air bleed will admit more air to the emulsion system and that can increase or decrease fuel flow to the engine. The size, number and location of the other air holes in the emulsion system, the size of the main well flow area, the size of the nozzle and the specific pressure difference at the moment are the determining factors. The ratios of air volume to fuel volume to flow area, with the air volume's expansion with the venturi velocity induced pressure reduction being the key. The bubbles expand as the pressure drop increases with airflow. Suck on an empty balloon to experience the effect.

The fuel flow through the main jet is the result of the pressure difference between the atmospheric pressure in the float bowl and the venturi air velocity induced vacuum acting on the nozzle and the main well. The venturi vacuum in the well is reduced (the pressure is raised) by the "air leak" from the air bleed. This reduces the pressure difference that causes the flow through the main jet. If the air bleed were big enough, the pressure in the well would be the same as in the float bowl and no fuel would flow. Think about drinking through a soda straw with a hole in it above liquid level. Bigger hole, less soda. Suck harder, not much more soda. Big enough hole, no soda. This is the means by which the emulsion system can "lean it out on the top end". Incidentally, the vacuum that lifts water up a soda straw is in the most sensitive operating range for emulsion systems.

It is in the lowest range of throttle opening, at the start of main system flow, that the effect of adjusting the introduced emulsion air (and it's effect in increasing the main fuel flow) is most critical. Small changes can have large and sometimes unexpected or counter-intuitive consequences. The goal is to seamlessly blend the rising main flow with the declining idle/transition system fuel delivery to accomplish smooth engine operation during opening of the throttle in all conditions, whether from curb idle or any higher engine speed. The high speed and load mixture correction is usually easily accomplished, in comparison.

The vertical location of the bleeds entering the main well influences the fuel flow in the following ways.

1: Orifices above float level or between the well and the nozzle allow bled air to raise the pressure (reduce the vacuum) in the nozzle and above the fuel in the well. That delays the initial start of fuel flow from the nozzle to a higher air flow through the venturi and is used to control the point in the early throttle opening where the main starts.

2: Orifices at float level increase low range (early throttle opening) fuel flow by carrying fuel with the airflow to the nozzle.

3: Orifices below float level increase fuel flow by the effect of lowering the level of fuel in the well to the hole(s) admitting air. This is like raising the float level a similar amount (increases the effect of gravity in the pressure difference across the main jet) and also adds to the airflow carrying fuel to the nozzle. Locating the orifices at different vertical positions influences this effect’s progression.

4: The "emulsion holes" influence is greatest at low flows and the "main air bleed" has most influence at high flows.

In the first three cases above, once fuel flow is established it is greater than it would be with fewer or smaller holes. Visualize wind blowing spray off of the top of water waves. It doesn’t take much pressure difference to cause the velocity of the airflow through the bleed orifices to have significant velocity in the orifice, even approaching sonic (1100 F.P.S.) if the orifices are small. The phenomena of critical flow is what limits the total air flow through an orifice and allows tuning by changing bleed size.

Essentially, the emulsion effect will richen the low flow and the air bleed size, main well and nozzle restrictions will control the increase or reduction of high flow. Again, the desired air/fuel ratio is the primary purpose of the bleed system. "Improved emulsion" is an oxymoron if the modification of air bleeds to "improve emulsion" results in an incorrect air/fuel ratio in some range of engine operation. Correct proportioning of all the different bleeds (and, of course, the idle, transition and power circuits) will give the correct air/fuel ratios over the total range of speeds and loads and a flat air/fuel ratio characteristic at wide open throttle.

Now, do you have any easy questions?
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Old 12-16-2011, 10:20 AM   #8
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Default Re: Carburetor guys...let's have a discussion on emulsions.

Mark, I'll admit that's alot for a Kentucky country boy to digest! Now what would be the simplification of what he said?
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Old 12-16-2011, 12:19 PM   #9
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Default Re: Carburetor guys...let's have a discussion on emulsions.

Also, I didn't see it mentioned anywhere, but would you tune a footbrake car different than a transbrake car because of the "transition" to wide open?
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Old 12-16-2011, 12:21 PM   #10
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Default Re: Carburetor guys...let's have a discussion on emulsions.

Did you read it a dozen times yet? At the bottom read from #4 down specifically. Emulsion has the most effect at the start of the mains but does have an effect on fuel flow at higher RPMs, MAB's primarily effects the higher RPM's but will affect the operation of the emulsion as well. When I went from .031 to .026 on the challenge I did so to richen the peak which it did, but it also leaned out the bottom slightly and essentially flattened the fuel curve a bit. Realize float level and fuel pressure have an effect as well.
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Old 12-16-2011, 12:31 PM   #11
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Default Re: Carburetor guys...let's have a discussion on emulsions.

Make the carb work well for the footbrake car, why would a t-brake car need to be different?
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Old 12-16-2011, 12:36 PM   #12
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Default Re: Carburetor guys...let's have a discussion on emulsions.

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Originally Posted by jmarkaudio View Post
Did you read it a dozen times yet? At the bottom read from #4 down specifically. Emulsion has the most effect at the start of the mains but does have an effect on fuel flow at higher RPMs, MAB's primarily effects the higher RPM's but will affect the operation of the emulsion as well. When I went from .031 to .026 on the challenge I did so to richen the peak which it did, but it also leaned out the bottom slightly and essentially flattened the fuel curve a bit. Realize float level and fuel pressure have an effect as well.
Okay so real world application here.....say I have a metering block that emulsions from bottom to top 32/30/28. Now, take the same block and change it to 28/24/20. That makes the first tip in of the main circuit leaner, and the top end a little bit fatter correct? EDIT: Also, about the footbrake/transbrake deal....I've always been under the impression that a footbrake car needs more fuel in transition to get the car to leave...especially if the converter is on the tight side.
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Old 12-16-2011, 02:09 PM   #13
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Default Re: Carburetor guys...let's have a discussion on emulsions.

In a footbrake car its more about getting the transition to WOT right. You will need to play with squirters and the t-slot to get it right. The better that all the circuits play together, the less squirter you will need.

If that stuff isn't right, when your t-braking it will not come up on the rev limitor as cleanly. I personally feel that not having these circuits right can effect launching off the t-brake. Think about if the carb is really rich going on the rev limitor(too much squirter), then you hit the rev limitor which creates misfires. Not an ideal situation to come off the rev limitor with.

Its about figuring out what the motor wants and needs and adjusting the fuel accordingly.
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Old 12-16-2011, 02:15 PM   #14
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Default Re: Carburetor guys...let's have a discussion on emulsions.

Man its a shame they did not have a school like Yellowbullet when I was a kid. I may have actualy went.
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Old 12-16-2011, 02:41 PM   #15
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Default Re: Carburetor guys...let's have a discussion on emulsions.

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In a footbrake car its more about getting the transition to WOT right. You will need to play with squirters and the t-slot to get it right. The better that all the circuits play together, the less squirter you will need.

If that stuff isn't right, when your t-braking it will not come up on the rev limitor as cleanly. I personally feel that not having these circuits right can effect launching off the t-brake. Think about if the carb is really rich going on the rev limitor(too much squirter), then you hit the rev limitor which creates misfires. Not an ideal situation to come off the rev limitor with.

Its about figuring out what the motor wants and needs and adjusting the fuel accordingly.
Makes sense. I THINK you can also drill a small kill bleed in the squirter boss in the metering block to kill the squirter after the initial "hit." From what I understand this is to keep it from pulling fuel out of the squirter going down the racetrack, on the transbrake, etc....also ideal for stock car engines where fuel mileage is a concern.
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