11 March 2018

SU carburetor | Construction | Working | Types | Application

SU carburettors, in general, a constant torque type carburettor. Zenith, Solex and carter carburettor are an example of this type.

SU carburettor differs completely from them being constant vacuum or constant depression type with automatic variable chock.

Construction and working of SU carburettor:

SU carburetor

SU carburettor consists of a sliding piston. The lower end of the piston is provided with a taper needle which is inserted into the main jet. When the piston is moved up and down the needle also moved up and down with the main jet. The upper end of the piston is given a flat from which is known as a suction disc. The up and down movement of the piston and the suction disc is guided by means of the piston rod and piston rod guide. 

The piston always remains loaded by a helical spring. The movement of the piston controls the air passage. The portion above the disk is called suction chamber which connects the air passage by means of slot provided in the piston. The Main jet of the carburettor can be moved up and down along the tapered needle by operating a lever from the dashboard. This moment is required to adjust the mixture strength throughout the operating range of the carburettor. The carburettor consists of an ordinary butterfly type throttle valve. The lower portion of this is connected to the atmosphere by means of a rectifier hole and the upper portion to the total throttle air passage. The system doesn't have any separate idling show running and accelerating system. 

Types of SU carburettors:

SU carburettor identification is made by letter prefix which indicates the float types :
H, HD, HS, HIF, HV, OM, KIF with different sizes include 1 to 1/8", 1 to 1/4", 1 to 1/2" 1 to 3/4" 1 to 7/8" and 2". 

SU carburettor applications :

  • SU carburettor was used in Rolls-Royce, Bentley, Rover, Riley, Turner and Aston-Martine, Jaguar, Triumph and also in Volvo. 
  • It also used in aircraft engines. 
  • Nowadays Hitachi also built carburettor based on SU carburettor technique that used in Datsun cars.