MrSciTrek said:
FOG said:
There is no "Butterfly" Only a inriching valves, the two are connected by a bar and cannot become miss adjusted.
FOG
Live & learn. Thanks Fog.
If you want to learn?
Look at this:
A description of how The CV carbs on your EX work.
Prepared for casual perusal by laymen
Definitions
CV Constant Velocity
Carb Short for Carburetor
Vacuum Pressure lower than atmospheric
Venturi A restriction in a pipe that causes an increase in air speed and a corresponding drop in pressure.
Atmospheric pressure
The weight of the Air all around you normally about 15 PSI
PSI Pounds per Square inch
Suction A bad word always misused to explain the force that is really a lower atmospheric pressure or a Vacuum.
Gravity See Isaac Newton
Jet A removable fixed size orifice used to regulate flow.
Float A device that displaces more fuel that it’s weight therefore it floats. Used to control the level of a liquid in a vessel.
Needle In the context of a Carburetor, A long tapered valve part (work with Jet)
Plenum A chamber used to store vacuum.
Pilot Circuit A system of jets, passages and valves used to supply small amounts of fuel at Idle.
Carb front The place where the air goes into the carb
Carb rear The place where the air exits the carb
Float bowl The fuel reservoir in the bottom of the carb
Slide The movable part that varies the size of the carb throat and carries the needle.
Diaphragm A seal to hold the vacuum in the Plenum.
Orifice The hole in something. Like a jet.
Equilibrium What nature strives to maintain at all times.
Description of carburetor function.
This design is an attempt at smoothing the running of a internal combustion engine, by means of varying the size of the orifice that the engine breaths through and thereby improving the atomization of liquid fuel at lower speeds. This is accomplished by utilizing the airflow into the engine to regulate the orifice size. This in theory at least produces constant velocity of the incoming airflow. By manipulating the small variations in atmospheric pressure created buy directing this airflow through a venture a slide is lifted and fuel is forced into the air stream .
As the air rushes in to your engine to fill the vacuum created by the downward motion of the piston, it is caused to flow through the carbs venturi, the resulting low pressure created by this flow is directly proportional to the air velocity. Atmospheric pressure now pushing down on the fuel in the float bowl causes fuel to well up thought the jet orifice this flow is regulated by the orifice size and the restricting needle. This same low pressure is transferred to a plenum chamber on the top of the carb. This vacuum lifts a slide connected to the diaphragm which forms the bottom of the plenum. As the slide is lifted it draws a tapered needle with it. As the slide rises the venturi gets larger which slows the airspeed and automatically reduces the low pressure or vacuum created. Equilibrium is achieved in this way, and air speed becomes constant.
This equilibrium is disturbed by a secondary restriction in the airflow into the engine. This movable restriction is called the throttle. As the restriction is eased the engine is allowed to run faster drawing in more air. This causes the slide to rise further to maintain equilibrium or constant air speed through the venturi. This is the process that regulates the flow of fuel into the engine.
By means of design, the needle attached to the slide increases the fuel flow proportional to the amount of air to maintain a burnable mixture.
Fuel Supply
In order for all the above to work, a constant level of fuel must be maintained in the float bowl (reservoir). This is accomplished by a valve operated by the motion of a float. The float rises and falls with the fuel level in the bowls, this motion opens the valve when it fall and closes it when it rises to a pre-determined level.
The valve is supplied by gravity from a tank above.
Pilot Circuit
All Carburetors have a glaring deficiency. That is poor fuel feed at low air Speeds. Even though these are called Constant velocity, there is a finite limit at the low speed end, where a carb big enough to supply the engine at high speed, cannot meter the fuel required at very low air speeds. (Idle). To accommodate this problem, a completely different fuel circuit is employed.
Just in front the throttle butterfly there are three small holes. A low speeds there is a strong vacuum in the area behind the throttle. The first of these holes is just exposed to this vacuum when the throttles are shut (at the Idle stop) . This vacuum draws fuel into the weak air stream from the float chamber. This flow is metered by the Pilot jet and further by the Pilot screws. As the throttle is opened further the additional holes are exposed to the vacuum and add there flow to the now larger air stream. Once the throttles are opened beyond a certain point the vacuum is lessened so much that the pilot circuit ceases to function.
Choke circuit
Another Misnomer, it’s really another mixture inrichner. When the engine is cold the tiny amount of fuel supplied by the normal running circuits is insufficient. This is because the fuel doesn’t evaporate quickly in the cold manifold and some that does is condensed on the cold walls of the manifold.
A third circuit called (ahem) the “choke” circuit supplies a gross amount of fuel needed to assure that enough of it is vaporized to run the engine. This flow in un-needed after a few seconds as the manifolds warm with the running engine. Part of the Choke mechanism is a cam that open the throttle a bit to raise the intake airspeed to a point where the main and pilot circuits take over.
I wrote that only to discover a better one here:
http://members.aol.com/roundr1/CVK40.html
FOG
