On Quick Fuel Q series carbs. I don't have one apart, but sketched what I am dealing with. Each metering block has 8 #28 jets for emulsion. What do they do exactly, and what part of the circuit do they effect?
Can someone explain emulsion tuning?
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These jets sit in the fuel with the other end of the passage exposed to the high speed air through the venturis which draws the fuel through these jets. These would be the main circuit. Idle mixture screws adjust the mixture at idle only. Once the carb is off idle, all the fuel is flowing through these jets. These are the jets you'd change to fine tune cruising and WOT lean/rich mixture.
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They pull air into the fuel to emulsify it.
If they were plugged, solid fuel would dump out the main venturis.
If they were plugged, solid fuel would dump out the main venturis.
No, you can change single jets as long as the manifold has a plenum
Huh ?? You're TOTALLY wrong. These jets sit at the bottom of the fuel bowls. They don't pull in air, they pull in fuel. If they're plugged, no fuel is getting by.
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emulsion ? ooh, I thought I read expulsion ... and here I thought it was designing a toilet bowl for a good, thorough flush each time ...
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Actually, the jets restrict the flow of fuel to the venturi, where the low-pressure area pulls the fuel in the main metering circuit.
Also worth noting that the type of carb is important. A vac secondary carb or carb with progressive secondaries will need to have the primary circuit adjusted (jet changes) at a cruise speed when the secondaries are closed. Check the plugs and change jets for optimal mixture. Then you need to make WOT passes and do the same on the secondary side. And since things don't mix perfectly in the plenum its not uncommon to change only the jet closest to the bank that's either lean or rich.
He's talking about the emulsion jets, not the main jets.
Emulsion jets and main jets are one and the same.
Ok.
Jcharger
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In a simple way, the main jets control the position of the whole high speed fuel curve and the emulsion jets control whether it rises or falls, in other words the shape of the high speed fuel curve. I would need to refresh my memory by doing more reading about how exactly to adjust them, but the principles relate to different parts of the curve and have an effect that cascades to other parts. When I looked at the shape of fuel curve on wide open throttle acceleration I found mine was actually pretty close out of the box in my case. In the end, I mostly tuned the air bleeds and main jets.
By that description, it sounds like they do the same thing as air bleeds?
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ABSOLUTE INCORRECT......refer to the basic operation of the emulsion device in a carburetor. Designs and appearance will differ between manufacturers, but thr simple explanation is: it causes the fuel (liquid) to begin the process of being vaporized to a gas, by mixing with air flow. Remember, the engine injests a vapor not a liquid to the combustion chamber.
The emulsion tube
When it comes to carburettors there are essentially two types each working on differing principles –the constant depression device or that of the fixed venturi, sometimes referred to as fixed jet. Because of their simplicity and ease of setting up, many vehicles in the past have been fitted with constant depression-type units, but where ultimate performance is required and although difficult to ‘tune’ – or as we now say, calibrate precisely – the choice is almost always that of the fixed jet or venturi principle.
The fixed-jet carburettor works by pulling fuel from a reservoir in response to a pressure signal from the venturi in the engine intake air. The depression thus created causes fuel to flow from the fuel reservoir in the carburettor while at the same time encouraging a small flow of air at atmospheric pressure to mix with the fuel. The fuel is metered through the main jet while the air is controlled through what is generally called the ‘air correction jet’. Somewhere in between, the fuel and air are intermixed to form an emulsion – a fine dispersant of the air inside the fuel. This assists the atomisation of the fuel as it eventually enters the engine airstream.
At times of low fuel demand, the air drawn in is very small and the fuel flow regulated by the main fuel jet will contain little in the way of an emulsion. With the throttle only slightly open, drops of liquid fuel will land on the throttle plate and atomise thereafter into the air. However, with increasing engine speed or load, as the fuel demand increases then the restriction of the main jet causes an increased depression in the air correction circuit, and this air passing through the emulsion tube effectively leans off the mixture: the higher the engine speed or load, the greater this air correction effect. Metering the fuel and the air is one thing, but mixing it and presenting it in a form so it readily mixes with the intake air is quite another. This is the function of the emulsion tube.
The essential points to remember are that the fuel passes around the outside of the emulsion tube at its base while air, coming from the top, comes down the inside of the tube and is extracted through a series of drilled holes of varying sizes and heights to mix with the fuel on the outside. When the engine is stationary, the fuel level will be the same as that in the float chamber, and will come to a level within the emulsion tube. As soon as fuel is demanded, the fuel level will drop in the chamber, uncovering more holes that will allow more air to mix, thus leaning the mixture.
As well as altering the size and height of these holes, it is also possible to alter the diameter and thickness of the emulsion tube in its cavity within the body of the carburettor. This acts as a restriction to the flow of fuel which, when all fashioned together, can tailor the flow of fuel more or less precisely to that required by the engine throughout its operating map. Under wide-open throttle acceleration the emulsion tube plays little part since the overriding effect is that of the main and air correction jet. At part-throttle however, when the quality of the fuel atomisation arguably has to be significantly better, the emulsion tube can be considered more critical. Understanding this and being able to apply it in practice is therefore one of the dying ‘black arts’.
Setting up a fixed-jet carburettor may be a long and often confusing business, but when the vehicle starts and drives smoothly and progressively, the satisfaction is immeasurable.
The write up uses English terminology from the U.K., (the King's English) but the principle is the same.
BOB RENTON
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If you go back to the first post the OP is CLEARLY referring to the main jets. Not every carb is equipped with changeable emulsion jets as pictured above - many just have fixed air bleeds.
Jcharger
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I just did a scan on the web and saw this, https://www.quickfueltechnology.com.au/technical-info/emulsion-channels
As I understand it, the air bleeds also do something to the tilt as well, but the emulsion is to fine tune in some way.
As I understand it, the air bleeds also do something to the tilt as well, but the emulsion is to fine tune in some way.
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No, I am well aware what a main jet is. I am referring to the 8 #28 emulsion jets/bleeds (whatever they are called) that are in each metering block of my Quick Fuel Q series mechanical secondary carbs.
EMULSION CHANNELS
Emulsion channels are what some would call the black magic of a carburetor - what happens here can be explained in several ways. The simplest illustration would be to imagine the fuel curve being moved up or down by the size of the main jet, and then the tilt or angle of the fuel curve being moved by the emulsion package. Many things go into the tuning the emulsion of a carburetor, which includes the high-speed air bleed (which supplies air to the emulsion orifices), the emulsion orifice size, number of orifices, and event he float level.
The hole size of each orifice is very critical in that the size of the hole will ultimately determine ho much air is to enter the main well - larger holes will yield leaner numbers. Going too far from a normal setting could cause you to adjust your jet size in order to maintain the car's behaviour - be sure to document or graph your adjustments and always note your baseline. Our carburetors and block kits offer a wide range of adjustability to help you reach your results. Pre-drilled and blank restrictions are available for tuning.
Emulsion channels are what some would call the black magic of a carburetor - what happens here can be explained in several ways. The simplest illustration would be to imagine the fuel curve being moved up or down by the size of the main jet, and then the tilt or angle of the fuel curve being moved by the emulsion package. Many things go into the tuning the emulsion of a carburetor, which includes the high-speed air bleed (which supplies air to the emulsion orifices), the emulsion orifice size, number of orifices, and event he float level.
The hole size of each orifice is very critical in that the size of the hole will ultimately determine ho much air is to enter the main well - larger holes will yield leaner numbers. Going too far from a normal setting could cause you to adjust your jet size in order to maintain the car's behaviour - be sure to document or graph your adjustments and always note your baseline. Our carburetors and block kits offer a wide range of adjustability to help you reach your results. Pre-drilled and blank restrictions are available for tuning.
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