SU Carburettor

The SU Carburettors Company

In 1905 Mr. George H. Skinner took out a patent for a carburettor in which both the air and fuel passages varied in accordance with the requirements of the, engine. The original design was a clean and simple layout in marked contrast to the multi-jet fixed choke carburettors and it provided a standard of flexibility and economy of operation hitherto unknown.

Engine Emission Control

The following features embodied in S.U. carburetters considerably reduce the harmful elements found in engine exhaust gases, and development resources at S.U. are concentrating on producing other improvements which will further assist in solving the pollution problem.

– Spring-loaded jet needle
– Overrun limiting valve
– Integral crankcase
– Ventilation control
– Temperature compensation
– Ball bearing suction chamber assembly.

Spring Loaded Jet Needle

The jet needle is retained in a predetermined position in the jet orifice by means of a spring loaded fixing. This ensures that the same shape and position of the orifice in carburetters of the same specification is maintained with subsequent repeatable emission values.

Overrun Limiting Valve

A precisely set spring-loaded plate valve is located in the throttle disc. The valve opens under high manifold depression conditions, i.e. overrun at closed throttle, reducing the depression and supplying a quantity of correct fuel/air mixture through the throttle disc. The correct combustion achieved reduces the value of hydrocarbon emission which would otherwise be emitted under these conditions.

Integral Crankcase Ventilation Control

Engine fumes and blow-by gases are drawn from the crankcase via a breather hose into the constant depression area between the carburetter piston and throttle disc, eliminating the need for a separate control.

Temperature Compensation (HS4 and HS8 models only)

Bi-metal discs, interposed between the jet and the mixture setting lever, move the jet to compensate for changes in mixture strength which occur with variations in temperature.

Ball Bearing Suction Chamber Assembly

This is the latest and one of the most important developments to be offered in the specification of a constant depression carburetter. The piston guide rod moves in a double row of ball bearings, thereby virtually eliminating the effects of friction and hysteresis. With this feature stability of carbon monoxide emission at idle speeds is achieved, together with further reduction of emission levels during acceleration and deceleration and improvement in repeatability of emission values.

* This assembly, the subject of a recent S.U. patent application; is available for 38.1 mm (1.5 in), 44-45 mm (1.75 in). and 50-80 mm (2.0 in) carburetters.

HS Carburetters

The competitively priced HS type (Horizontal Short body) is the latest of a long line of side mounted float-chamber S.U. carburetters. The jet is fed by a flexible nylon tube from the base of the float-chamber and vertical movement of the jet provides cold start enrichment.

The HS type is available for both single and multi carburetter applications complete with all necessary connecting linkage in throttle bore sizes ranging from 31’75 mm (1•25 in) to 50•8 mm (2’0 in). They may be mounted at angles ranging from horizontal to 30° downdraught and are available with solid or flexible float- chamber mountings.

Features developed for the control of exhaust emissions described on the previous page can, except where specified, be embodied in the full HS range.

HS Features.

– Proved constant depression principle
– R.H. or L.H. float-chamber mounting
– Flexible or solid-mounted float- chamber
– Three controls:
– mixture adjustment
– slow run
– fast idle

HIF Features

– Proved constant depression principle
– Integral float-chamber
– Float concentric to jet
– Fuel viscosity compensator
– Part throttle bypass emulsion system
– Rotary valve cold-start enrichment device

 Three controls:

– mixture adjustment
– slow run
– fast idle
– Overrun limiting valve
– Easy accessible mixture adjustment
– with sealing facility
– Spring-loaded jet needle assembly
– Crankcase ventilation control
– Alternative float-chamber vent positions
– DU throttle bushes and rubber seals

The HIF type is available for both single and multi carburetter applications, complete with all necessary connecting linkage, in throttle bore sizes of 38.1 mm (1.5 in) and 44-45 mm (1.75 in), and may be mounted at any angle from horizontal to 40° downdraught inclusive.

Most of the exhaust emission features detailed earlier are fitted as standard on the HIF range.

The HIF carburetter is the most recent type to be added to the S.U. range and when equipped with the ball bearing suction chamber assembly represents the very latest in constant depression carburetter design.

About Zaighum Shah 90 Articles
Zaighum Shah is a mechanical engineer having more than 20 years of experience. Zaighum is specializing in product development in Sugar Mill industries. Zaighum has gone through all phases of mechanical engineering and it’s practical implementation. Zaighum has been solving most complex problems, designing new systems and improving existing models and systems.