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. Once I confirm (and correct, if needed) fuel level, will look at pump jet size and acceleeration pump performance to see if I am missing something there.What is an emulsion tube and why do I care? The definition of the word emulsion is to mix. Idles like a champ at 750, hard acceleration runs 15.5 to 16.5 on AFM, flutters and farts on deceleration (super lean), typical transition miss from idle to mains. My specs: triple 40 DCOE carbs, 30 mm venturis, auxiliary 4.5, idle jets 50F9, main jet 125, air corrector 175, pump jet 45, pump exhaust valve 050, emulsion tube F11, float needle valve 1.75. Also, goes very lean on hard acceleration, then richens as the main jets kick in. I am getting fuel dripping off the front of my air horns, in some cases. My 40's are dripping off the pump jet in a number of the chambers, part due to the pump jet cover not being screwed down tight enough, but I need to confirm the fuel level to make sure this is not contributing to the problem. Here is where I think the vacuum pulls on the accelerator nozzle and causes the greatest fuel leak at cruise: The red numbers show the change in Air:Fuel Ratio at each corresponding RPM. (plugged vs non-plugged during slow accelerations (2 min.) to prevent activating the accelerator circuit). My next project will be ITB's and Mega squirt.įYI here is data from my friend showing the AF ratio and proving a leaking accelerator circuit. You will have to wait until I get Mikunis. adjust the accelerator circuit for slow and fast RPM transitions install the accelerator circuit jet/ball valve AND add springs to press the weights down OR replace the weights with springs.ħ. install the mains and tune for high rpm and WOT performanceĦ. experiment at low rpms and tune the idle circuit for idle and low rpm operationĥ. set throttle linkage so that valves are covering the first progression hole.Ĥ. plug inlet jet/ball valve leak back to accel. At present, here is what I would do with Weber DCOE's to tune.ġ. I speculate that the engine vibration shakes the weights and allows fuel to pass AND there is a vacuum at at accelerator circuit's nozzle at partial throttle as the top of the throttle valve approaches the tail of the main venturi. One of the problems I found in working with an experimenter on the side draft forum is that the accelerator circuit leaks fuel all the time and it lowers the air:fuel ratio. I have a set of Webers here that I will experiment with once I break in a resto's engine. I have been meaning to update this article with tuning guidance following further study on a side draft forum but the data I have so far is inconclusive.
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