Quote:
Originally Posted by HWYSTR455
Emulsion bleed tuning really is more useful in drag or circuit racing, when you have some gear more towards one side of the spectrum and specific demands. For 'general' street strip stuff, you can get by with the out of box bleeds.
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I want to mention this part, since it's part of the wackiness we see in modern carbs. For decades, the stock Holley carbs on production cars like Ford 390s had a small number of small emulsion bleeds in the metering block. Those were either 2 vertical bleeds into the main well, or the bleed tubes that are inside the main well. The upper hole right below fuel level controls pullover, and the hole about 1/2 down from that helps shape the fuel curve once the mains get going. Those 2 holes, along with the high speed air bleed and the main jet, control the main circuit fuel curve.
There were a few cases where adding a 3rd hole between the two would add fuel at part throttle, heavy load conditions for racing. Adding emulsion air to the main well lifts fuel and makes it richer, especially at low to moderate venturi airflow. The fuel is lifted by the bubbles, so it takes less venturi signal to flow fuel. This makes the curve richer until venturi draw gets stronger, and then the air through the bleed system starts to displace the fuel and the delivery leans out. The rate of fall in the wells depends on the size of the main jet. Smaller the jet, the faster the fuel falls and uncovers additional bleed(s). This is how the jets, emulsions and the HSAB add or remove fuel from the main circuit.
Then the aftermarket figured more is better, and now you have 3, 4, 5 emulsion holes in the main well of aftermarket billet metering blocks. "Out of the box" bleeds are now out to lunch for a mild street motor.
This usually results in rich fueling from 2300-4000 RPM, when on the mains at part throttle. Then when you got to WOT, the mixture leans out too much as the air displaces the fuel in the main well. You can't add enough jet or power valve to richen it back up at WOT, without rolling coal at 3000 RPM.
The solution is set the top hole and the 3rd hole at .028" and block all the others. That recreates the old-school setup from the 1960s. That usually helps get the main circuit back under control. Then sizing the main jet, HSAB and the fuel level starts the mains at the correct time and keeps it from curving rich/lean at WOT. You see this if you follow the curves from the chart.
The most interesting thing is look at the effect of the HSAB. (Some call it a MAB, I call it a HSAB and I aim to kill yo with it- Karl from Sling Blade)
Conventional wisdom is that the larger the high speed bleed, the later the mains start and leaner it is everywhere. However, a larger bleed will blow air through the emulsion well and the main well at low venturi signals. Those bubbles lift the fuel up to the booster and now its flowing fuel. This will actually start the mains EARLIER and make it RICHER, until the system starts to displace fuel in the wells with bleed air. At that point, it swings violently lean, cuz it taint got no gas in it. Its all about the total amount of air available from the HSAB, the size AND location of the emulsions in relation to the fuel level in the well and how hard the booster is pulling on the well.