Although fuel readily evaporates, air cannot be saturated with enough fuel vapor needed for engine combustion. This means that liquid fuel must be mixed with the air, or atomized. Proper atomization of fuel is the key to successful tuning. Introducing fuel into the air as a fine mist in specific ratios is what we need the carburetor to do. It's difficult to atomize fuel into air using only a variable stream of air as the pressure source. There is fairly wide leeway for fuel atomization quality to be "good enough" for engine combustion, but fuel atomization needs to be nearly perfect to deliver optimum power. Liquid fuel does not stay suspended in air for very long, and even worse, turbulence within the manifold causes the fuel droplets to crash against the insides of the manifold, increasing the difficulty of keeping fuel mixed with the air consistently. Though these are problems inherent to any engine, unless the carburetor is jetted completely wrong, these occur at low enough RPMs where it's not too much of  concern.

  Air flows through the venturi, or "barrel" of the carburetor. The nature of the venturi is such that as air flows through it, there is a pressure drop created at a point inside it. There is also a mini, "booster", venturi set down into the primary venturi. It amplifies the pressure drop, helping to draw fuel in at low RPMs, when the air flow is lower. Inside the booster venturi is the fuel pipe. It is located at the point where the pressure drop is the strongest. It is also located above the fuel level in the float bowl, otherwise fuel would simply spill out into the venturi. The fuel pipe comes up from a circuit at the bottom of the float bowl, where the fuel jet limits the amount of fuel that can flow up the fuel pipe.

When air flows through the venturi, the pressure at the end of the fuel pipe becomes less than the atmospheric pressure acting on the fuel in the float bowl, causing fuel to spill out of the fuel pipe and be carried into air flowing into the engine in a mist. This is sometimes referred to as the "fuel signal". As the flow of air through the venturi increases, the pressure at the fuel pipe decreases, creating a more powerful signal. The pressure drop is not linearly proportional to the flow through the venturi; the pressure decreases at a higher rate than the air flow increases. This means that the ratio of fuel to air increases as air flow through the venturi increases. But the carburetor has a way to "bleed off" some of that powerful signal; the "Emulsion System".

For each barrel, the emulsion system consists of a thin brass tube that runs from the top of the main circuit down through the same path that the fuel tube  uses. It has an air jet on the top, which sits far above the level of fuel in the float bowls, and the bottom half stays submerged in fuel. At the bottom of the emulsion tube is a series of holes drilled cross-ways through it. As air flows inside the booster venturi, the pressure differential created vacuums out fuel from the pipe. When the vacuum becomes great enough, it begins to also suck air down into the main fuel circuit from the air jet located at the top of the emulsion tube. This results in the outgoing fuel being laden with air bubbles which helps the quality and consistency of fuel atomization. The size of the air jet on the top of the emulsions tube dictates the threshold of the vacuum needed to pull air into the main fuel circuit.

Arguably this is the system's primary job in the carburetor (hence it's name), as fuel atomization is of the utmost importance in carburetion. But an equally important job that the emulsions system does is bleed off some of that overbearing signal to the main circuit when air velocity through the venturi becomes high enough to draw too much fuel into the air stream. In fact, if the emulsion system were blocked (air jets plugged), as the air velocity was slowly increased, the pressure differential would eventually become great enough to siphon raw fuel right into the carburetor. The signal to the main circuit is bled off, or corrected by jets located in the tops of the emulsion tubes. These jets are commonly referred to as "air bleeds", "air jets", or "correction jets".