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The effect of the emulsion tube will depend on the hole pattern. Here is how to read it: First, hold the emulsion tube upside down and inspect the hole pattern. Holes at the top of the emulsion tube will affect the top-end of the rev range. Holes in the middle will trim the mid-rpm range, and holes at the bottom, the low-rpm range. Where there are no holes, the mixture will be rich. Where there are holes, the mixture will be leaned out. Just how much the mixture is leaned out by the presence of holes depends on how many, and how big. The more holes present, the more the mixture is leaned out at that point. Because it is fed with air from the air bleeds, the emulsion tube's overall function is influenced by the air bleed size. A larger air bleed leans out the mixture, but at low rpm and small throttle openings, the air bleed has little influence over the mixture. As the engine's demand for air increases due to an increase in throttle opening and rpm, so the air bleed's influence increases. At high rpm, just a few thousandths change in the air bleed diameter can have a significant effect on mixture.One other aspect of the emulsion tube and well is that they act not only as a means of calibration but also as a control element for fuel atomization. By emulsifying the fuel prior to it reaching the booster, the fuel is easier to shear into fine droplets at the point of discharge. Generally, the more it is emulsified with air in the emulsion tube, the easier it is to atomize at the venturi.
Emulsion tubes control the metered fuel and air introduced into the Carburetor. When air enters the emulsion tube through the air jet and fuel enters through the the main fuel jet this condition emulsifies the fuel delivered into the carburetor. The emulsion tube has a series of small holes from top to bottom which regulate the fuel mixture. These holes allow air and fuel to enter the main circuit and emulsify fuel. Low speed engine conditions or engines at idle do not require use of the emulsion tube or the main circuit. As engine speed increases the fuel level in the float bowl drops uncovering these holes and allowing air from the air jets to enter the main circuit resulting in a lean mixture. As the engine speed increases the fuel level in the float bowl continues to drop. This uncovers even more of the holes in the emulsion tube, which makes the air jet have a greater effect on the low to high rpm fuel delivery mixture.
From memory, as the air and fuel are flowing at low speed, the air only enters the emulsion tube through the holes high up, but as speed increases, the air travels further down the well.If the top holes are to big, to much air enters the tubes at the top at high speed and does not mix well thus giving poor fuel delivery quality, if they are to small, not enough enters at low speed, giving poor fuel delivery quality.Also, the bigger the air leak into the emulsion tube via the air correction jet and the emulsion tube holes, the leaner the mixture as the pressure drop across the main jet is reduced and there is more air introduced to the metered fuel.