[Tom Vaught]

A bit more on Emulsion Circuits on Holley Carbs

A Old Holley Carb had (as I previously showed) a metering block with two emulsion holes on each side of the metering block.
(The newer carbs have 3 emulsion holes per side, 4 holes per side, and even 5 holes per side.)

First off You need to understand a couple of circuits on a carburetor the Booster Circuit and the Emulsion Circuit.

I earlier spoke about the Booster Circuit as having several options on a Holley carb:
Basic Straight Leg "Crossbar" Boosters, Down Leg Boosters, Stepped Downleg Boosters, and Annular Discharge Boosters.
A Booster just take a venturi signal to the Main Jet and makes the Main Jet Signal bigger. (An Amplifier of the Main Jet Fuel Circuit Signal).
Three big things control how well a Booster works:
1) The Booster Design: Annular, Down Leg, Aerosol, etc
2) What the entry and the exit of the Booster looks like and how well was it designed
3) Where the Booster is placed in relation to the carbs venturi or lack of a venturi (3-BBL)

That being said we move on to the Emulsion Circuit: I also spoke on that a bit earlier, too.

We used to have a Very Smart Carb Guy from "Down Under" (Australia) named Shrinker on the Motorsports Board who said several times:
"You really don't need Emulsion Circuits if you do your job right." (Have to agree somewhat on that deal).

I posted before about OLDER HOLLEY CARDS having two Emulsion Circuits. Then Holley did a 3 circuit, 4 circuit, 5 circuit.
There was a reason why they did that!

Shrinker's Words: "Emulsion is a correction for incorrect vacuum performance from a booster. It is also a correction for incorrect main jet design. Carburetors can, and are, quite successfully used without emulsion. However the carburetor must be specifically tuned to each engine more accurately if its a no emulsion design. Using a design with no emulsion is not a carby suitable for hotrodders. It takes a high level of machining accuracy and a lot of testing to achieve a desired result without emulsion. It is very easy to alter fuel curves etc with emulsion. Using emulsion is cheap, easy, bulk mass production techniques."

I have seen Governor Carbs on Medium Duty Trucks (and a limited rpm range on the main circuit) that only had ONE Emulsion Hole.
But as Shrinker posted "A Zero Emulsion Carb is not a carby suitable for hotrodders". Holley did stuff for a reason on Commercial Vehicles vs Hot Rods.

1) It is very easy to alter Fuel Curves with Emulsion Circuits. Getting it right takes tons of effort (as I mentioned on NASCAR Carbs).
2) Emulsion Holes are cheap to do to a metering block and gives Hot Rodders and people who later FIX Hot Rodders carbs something to do.
(Remember, I took "screwed up carbs" and many times put them BACK to Holley's Build Specs and they Worked Great again.)

In simple terms, Emulsion Holes create air bubbles that lower the fuel density, The lower density fuel "floats" above the normal fuel.
That causes the lower density fuel to have a higher fuel surface level than normal density fuel.

Once the fuel surface level is up to the height of the outlet tube it can flow to the booster. At that point the engine starts to run on the fuel.
At low air flow levels thats the physics behind the Emulsion Circuit. You are using air to make the surface of the fuel closer to the discharge outlet.

At higher flows through the carb the main jet restriction causes a reduction of the liquid level in the well and that lower level uncovers some Emulsion Hole Bleeds. When that happens, the air flow through the bleeds blows the fuel along its path. The amount of "blow thru" is controlled by the Main Air Bleed and the sizing of the various Emulsion Bleeds.

Under Acceleration, when the fuel flow into the bowl causes a lowering of the level (high fuel demand). The pressure on the entrance to the main jet is changed, so the flow rate of the jet is changed and that in turn changes the level of fuel in the main well.

You really have to be "on your game" to be successful when messing with Emulsion Jet changes.

More Later.

Tom V.