| Carburetor Q&A.....
Given that a four-barrel carburetor possesses something in the order of 200 components to allow it to function correctly, itís no wonder the average enthusiast has the odd question about how it operates and why. Words and phrases like atomization, vacuum signal, fuel-metering circuits, etc. can be a little bewildering. So, here are a few of the basics with several useful illustrations to help explain. This article contains information that applies to a wide range of V8-engined machines, from street cars to tow vehicles, and from oval track racers to drag strip cars.
1) Q. Is air pushed or sucked into a carburetor?
A. With the exception of forced induction systems (centrifugal supercharger, or turbocharger - where air is forced through the carburetor), air is drawn through the carburetor (sucked) by the engineís vacuum signal. The amount of air is determined by the strength of the vacuum signal.
2) Q. What is the difference between the straight-leg venturi booster, the down-leg booster, and the annular-discharge booster? Also, when should one be used in preference to another, and how does it affect jetting?
A. A straight-leg booster
has, as its name implies, a straight leg, which protrudes from the body of the carburetor into the main venturi. Its discharge ring is situated slightly above the venturiís most effective zone. Its discharge ring is slightly above the venturiís most effective zone. The color red indicates the main fuel circuits, which connect with the main jets, the emulsion holes (blue) and the high-speed air bleeds located in the air entry on top of carburetor. The color yellow indicates the idle-fuel circuits, which connect with main-fuel wells, the idle-feed restrictors, the idle-air bleeds (also located in air entry on top of carb), and the idle-discharge ports and transfer slots in the baseplate.
B. A down-leg or drop-leg venturi booster
drops the discharge ring lower in the carburetorís main venturi where it operates in air of higher velocity, which draws mot="_blank">Barry Grant Inc.