In the previous articles, we have discussed the automobile Carburetors Solex and the Carter Carburetors. These Carburetors are constant choke Carburetors. But this S.U Carburetor can adjust the choke to maintain the constant vacuum. Let’s discuss more in detail with a schematic diagram of an S.U Carburetor.
S.U Carburetor is a constant vacuum with an automatic variable choke. There are three different types of Carburetors available in the market. the H-type, HD-type(Diaphragm-jet), HS-type and the DU6-type (dual choke) is in limited quantity. Out of these, the H-type is the most familiar type Carburetor. We are going to discuss the H-type in this article.
S.U Carburetor Construction
- S.U Carburetor consists of a sliding piston and the tapered needle inserted into the main jet.
- Along with the piston upward and downward movement, the needle and the main jet also moves.
- There is a suction disc attached to the upper end of the piston.
- Piston rod and the piston rod guide help to guide the piston and the suction disc as shown in the schematic diagram.
- The piston is loaded with the helical spring.
- There is this portion above the suction disc is called the suction chamber which will be connected by the air passage by means of a slot provided in the piston.
- And there is an ordinary butterfly throttle valve as shown in the above fig.
- There is an air rectifier hole provided at the lower portion of the suction disc and the upper portion of this disc will be connected to the throttle air passage.
S.U Carburetor Working principle
This Carburetor does not have different engine operating condition such as the idling and the slow running(cruising), normal running, accelerating.
As the piston is loaded with the helical spring and the weight of the piston will be also supported by the vacuum in the suction chamber. the position of the piston will be balanced by maintaining the constant vacuum in the suction chamber. if any deviation occurred the piston gets moved up/down.
There will be a lever attached to the main jet to control the fuel flow while the engine needs to start. Since engine starting needs a richer mixture.
The throttle is opened more the more air is allowed to pass thru through the inlet due to upward movement of the piston. the upward movement of the tapered needle also ensures the more fuel flow from the main jet. This is how the air and the fuel passages are varied with the different engine speeds and velocities of the fuel and the air remains constant. in this system.
This is how an S.U carburetor works.
We have discussed the S.U Carburetor how it works for the different engine speeds with the lever. Since it doesn’t have a separate engines speeds such as the idling and the slow running(cruising), normal running, accelerating. Let us know your thoughts in the comment section below.