![]() Air holes that are drilled at different angles and sizes not to mention how many holes. Emulsion tubes are a complex part with diameters and steps in the diameters. Now that you know what's going on, let's look at some tubes. Now you can see what is happening here so if you want more fuel to sit in the well you would get a smaller diameter tube. You have less water with the ping pong ball glass don’t you? Get it? Ok back to carbs. Now do the same thing but use a ping pong ball instead of a marble. ![]() ![]() You have a glass and you put a marble in the glass now you fill the glass half way up. Now the emulsion tube displaces some of the amount of fuel and the bigger the tube the less fuel you have. We have “x” amount of fuel in the well determined by the float level. So if you’re not sure, you should check it. I don’t mean wrong to my specs, I mean wrong according to their own specs. Other brands can be off too but I’m telling you the webbers most of the time are wrong. Brand new webbers are wrong out of the box. I very rarely see them set right out of the box. This amount that is sitting in the well will get dumped down the throat of the carb when we first get into the main circuit. So whatever the fuel level is in that chamber it also is in the well. The cast in tube or well is connected to the float bowl chamber via a hole at the bottom of the well. First, and oh so important, is the fuel level in the bowl. The amount of gas is determined by two things. As I said earlier the emulsion tube sits in a well. This amount of fuel is very important to how the engine performs. So unmixed fuel gets dumped first? Is that what I'm reading? Yes it is. That mix then comes out of the auxiliary venturi. Once the well is dry then gas is pulled up through the main jet and air is pulled down through the air jet and mixed. Once it is strong enough it will pull fuel out of the well. As you get into the throttle a vacuum signal forms under the auxiliary venturi (booster). Let’s look at how the main circuit works then it will explain what the emulsion tube does. Still with me? Here are some pictures to show you what im talking about. ![]() In other words, gas comes up from the bottom of the well through the main jet that is in the bottom of the emulsion, tube then air comes down through the top and then that mixture comes out the side into the throat of the carb. That is where the main circuit comes out. If you were to look in the side of the well of the carb you will see a passage that leads out to the auxiliary venturi or as the V8 world calls it the booster. Ok so that is how the gas gets into the well that the emulsion tube sits in, what about the air? The air is going to come down through the tube holder and then the air jet that is in the top of the emulsion tube and out the middle of the tube through some holes that have been drilled in the side of the emulsion tube. The bowl is where the gas is kept in a carb until it is needed. This hole is part of a passage that leads to the bowl. It sits in a tube so to speak that is part of the body (casting) of the carb. So after this article you might want to think about changing them or simply look at what you have and know you have the right tube for what I am doing. The nice thing about the tubes in the IDF and some other carbs is they are changeable. The theory here will apply to other carbs as well. I will be talking about the tubes found in the Weber IDF carbs that are most commonly used. This is a tube found in a carburetor that mixes fuel and air for the main circuit. What is an emulsion tube and why do I care? The definition of the word emulsion is to mix.
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