Editing Carburetor

[[Image:Autolite 4 barrel ford small block.JPG]]

Autolite 4 barrel as used at Ford [[smallblock]] 1967

Essentially a carburetor is a solution to the problem that fuel comes in liquid form and needs to end up as a vapor to be combusted.  Generally a carburetor is bolted to the top or side of an intake manifold (depending on the type) and uses the air rushing into the engine to atomize gasoline released from a port or "jet."  Different brands of carburetors accomplish this in several slightly different ways, but the concept is the same for all.

Carburetors encounter various problems through the course of operation such as temperature, transition of throttle, amount of throttle etc.  For this reason, they have more than one "circuit."  A circuit is a method of adding gasoline to the rushing intake air so that it can be atomized.  

When idling, a carburetor uses the idle circuit.  This is most often a needle valve which allows a small amount of fuel to pass into the bore of the carburetor from the fuel bowl under idle condition.  

Next, a primary circuit using different sized jets (and sometimes vacuum actuated rods inside the jets) responds to increased fuel demand (in the form of intake flow velocity) with more fuel allowed into the carburater bore.  

Under high-throttle conditions, some carburetors are equipped with a secondary circuit, which is essentially another set of jets (similar to the primary circuit) which allow even more fuel into the intake charge.

A transition circuit, often referred to as an "accelerator pump" squirts fuel into the rushing intake charge and is actuated by positive movement in the throttle.  For example, when pressing the accelerator from 1/4 position to 3/4 position, the accelerator pump squirts an amount of fuel proportional to the amount of accelerator travel into the carburetor bore.  This amount can be modified by accelerator pump cams as well as a number of other methods depending on the brand of carburetor.  The accelerator pump is also used to add fuel for initial starting in many cases (as when "pumping" the gas on a cold motor).

Under cold coditions, a choke circuit can be used which increases the amount of fuel in the intake charge.  This is a solution to the problem that gasoline does not atomize well when it is cold.  This circuit is inactivated either manually or by an electronic actuator when the engine reaches operating temperature.

Carburetors can contain other circuits such as power valves (vacuum dependent).  Again, the reason for every circuit that a carburetor has is to provide a mechanical fix for operational/environmental challenge.