308:. The slide carburettor has the same piston and main needle as an SU carburettor, however the piston/needle position is directly actuated by a physical connection to the throttle cable rather than indirectly by venturi airflow as with an SU carburettor. This piston actuation difference is the significant distinction between a slide and an SU carburettor. The piston in a slide carburettor is controlled by the operator's demands rather than the demands of the engine. This means that the metering of the fuel can be inaccurate unless the vehicle is travelling at a constant speed at a constant throttle setting - conditions rarely encountered except on motorways. This inaccuracy results in fuel waste, particularly as the carburettor must be set slightly rich to avoid a lean condition (which can cause engine damage). For this reason
233:
225:
279:
of the function is determined by the profile of the needle. With appropriate selection of the needle, the fuel delivery can be matched much more closely to the demands of the engine than is possible with the more common fixed-venturi carburettor, an inherently inaccurate device whose design must incorporate many complex fudges to obtain usable accuracy of fuelling. The well-controlled conditions under which the jet is operating also make it possible to obtain good and consistent atomisation of the fuel under all operating conditions.
17:
275:
upwards, increasing the size of the venturi, until the pressure drop in the venturi returns to its nominal level. Similarly if the airflow into the engine is reduced, the piston will fall. The result is that the pressure drop in the venturi remains the same regardless of the speed of the airflow - hence the name "constant depression" for carburettors operating on this principle - but the piston rises and falls according to the rate of air delivery.
399:
168:
342:
334:
25:
297:
operation - increasing the supply of fuel so that the carburettor will deliver an enriched mixture at all engine speeds and throttle positions. The 'choke' mechanism on an SU carburettor usually also incorporates a system for holding the throttle plate slightly open to raise the engine's idling speed and prevent stalling at low speeds due to a rich mixture.
293:, which requires periodic replenishment. The damping is asymmetrical: it heavily resists upwards movement of the piston. This serves as the equivalent of an "accelerator pump" on traditional carburettors by temporarily increasing the speed of air through the venturi when the throttle is suddenly opened, thus increasing the richness of the mixture.
274:
If the airflow into the engine is increased - by opening the throttle plate (also known as the "butterfly"), or by allowing the engine revs to rise with the throttle plate at a constant setting - the pressure drop in the venturi increases, the pressure above the piston falls, and the piston is pushed
270:
in the venturi. This pressure drop is communicated to the upper side of the piston via an air passage. The underside of the piston is open to atmospheric pressure. The difference in pressure between the two sides lifts the piston. Opposing this are the weight of the piston and the force of a spring
278:
Since the position of the piston controls the position of the needle in the jet and thus the open area of the jet, while the depression in the venturi sucking fuel out of the jet remains constant, the rate of fuel delivery is always a definite function of the rate of air delivery. The precise nature
271:
that is compressed by the piston rising. Because the spring is operating over a very small part of its possible range of extension, its force is approximately constant. Under steady state conditions the upwards and downwards forces on the piston are equal and opposite, and the piston does not move.
471:
Standard S.U. carburetors (American spelling) were also a popular upfit for Harley-Davidson motorcycles, given their space saving "side draft" design and superior ability to self-compensate for changes in air density/altitude. Many owners replaced the stock
Linkert, Bendix or Keihin carbs with SU's
296:
SU carburettors do not have a conventional choke flap, which in a fixed-jet carburettor enriches the mixture for starting the engine from cold by restricting the air supply upstream of the venturi. Instead a mechanism lowers the jet assembly, which has the same effect as the needle rising in normal
324:
One of the downsides of the constant depression carburettor is in high performance applications. Since it relies on restricting air flow in order to produce enrichment during acceleration, the throttle response lacks punch. By contrast, the fixed choke design adds extra fuel under these conditions
104:
Following the outbreak of war in 1914, carburettor production nearly stopped, with the factory making machine gun parts and some aircraft carburettors. With peace in 1918, production resumed, but sales remained slow and the company was not profitable, so Carl
Skinner approached his customer,
356:"H": introduced in 1937 in which the float bowl has an arm cast into its base, which mounts to the bottom of the carburetor with a hollow bolt or banjo fitting. Fuel passes through the arm into the carburetor body. The bolt attaches to the carburetor body just behind the main jet assembly.
386:
To determine the throat size from the type number: If the final number (after one, two or three letters, beginning with H) has 1 digit, multiply this number by 1/8", then add 1". For example, if the type number is HS6, the final number is 6: 6/8 = 3/4", add 1, total is 1-3/4", etc.
89:, London, manufacturers of their carburettor. Herbert continued to develop and patent improvements through to the 1920s, including the replacement of the leather bellows by a brass piston, even though he was a full-time director and divisional manager of Lilley & Skinner.
361:"HD": introduced in 1954 with the float bowl mounted with its arm fastening directly below, and concentric with, the main jet. The arm has a flange that fastens with 4 screws to the bottom of the carburetor, and sealed with a rubber diaphragm integral with the main jet.
109:, and managed to sell him the business. Carl Skinner (T. C. Skinner) became a director of Morris's privately held empire, and remained managing director of S.U. until he retired in 1948 aged 65. Production was moved to the W. R. Morris-owned Wolseley factory at
69:(1872–1931), pioneer motorist and an active participant in the development of the petrol engine, invented his Union carburettor in 1904. His much younger brother, Carl (Thomas Carlisle) Skinner (1882–1958), also a motoring enthusiast, had joined the
366:"HS": introduced in 1958 the float bowl can be rigidly or rubber mounted to the main body, fuel is transferred by an external flexible pipe to the jet. The jet moves down to enrich the mixture for cold starting,when the 'choke' linkage is pulled.
312:
motorcycle manufacturers ceased to fit slide carburettors and substituted constant-depression carburettors, which are essentially miniature SUs. It is also possible - indeed, easy - to retrofit an SU carburettor to a
517:
In 1929 SU introduced the
Petrolift electric fuel pump, which could be fitted as a substitute for the vacuum type pumps common at the time. This was superseded in 1932 by the L type fuel pump, which used a
97:
S. U. Company
Limited — Skinner-Union — was incorporated in August 1910 to acquire Herbert's carburettor inventions, and it began manufacture of the carburettors in a factory at Prince of Wales Road,
300:
The beauty of the SU lies in its simplicity and lack of multiple jets and ease of adjustment. Adjustment is accomplished by altering the starting position of the jet relative to the needle on a fine
918:
SU Carburetors Owners
Workshop Manual by Don Peers: Part 1 Chapter 2 and Part 2 Type H, Haynes Publishing Group, Spsrkford YEOVIL Somerset England. Copyright JH Haynes and Company Limited 1976
555:
S. U. Company
Limited, 386—388 Euston Road, N.W. Capital £5,000 in £1 shares. Formed to acquire from G. H. Skinner certain inventions relating to carburettors for motorcars &c
147:, which incorporated an entirely new company with the name The S.U. Carburetter Company Limited, which continues to manufacture carburettors, pumps and components, mainly for the
582:
which was imported into
Knowledge before November 2008 and is therefore validly licensed for use on Knowledge. All relevant terms must be followed. The original article was at
263:, so the movement of the piston controls the amount of fuel delivered, depending on engine demand. The exact dimensions of the taper are tailored during engine development.
259:
into the airstream passing through the carburettor. Since the needle is tapered, as it rises and falls it opens and closes the opening in the jet, regulating the passage of
673:
H. Jones: Herbert
Wakefield Banks Skinner. 1900-1960. Biographical Memoirs of Fellows of the Royal Society, Vol.6, (Nov. 1960), pp.259-268, publisher: The Royal Society
129:
Manufacture continued, then by The S. U. Carburetter
Company Limited, which was incorporated 15 September 1936, as part of the Morris Organisation, later known as the
304:(26TPI for most pre-HIF versions). At first sight, the principle appears to bear a similarity to that of the slide carburettor, which was previously used on many
579:
390:
If the final number has 2 digits, it is the throat size in mm. For example, if the type number is HIF38, the final number is 38, size is 38 mm etc.
81:, South Kensington in 1934. In 1905, Herbert applied for a patent, which was granted in early 1906. Later, Carl sold his interest in footwear business
380:
The
Imperial sizes include 1-1/8", 1-1/4", 1-1/2", 1-3/4", 1-7/8", and 2", although not every type (H, HD, HS, HIF) was offered in every size.
383:
There were also H models made in 2-1/4" and 2-1/2", now obsolete. Special purpose-built carburetors (Norman) were made as large as 3".
986:
966:
881:
682:
282:
This self-adjusting nature makes the selection of the maximum venturi diameter (colloquially, but inaccurately, referred to as "
106:
371:"HIF": (1972) the float bowl is horizontal and integral (hence the name) Horizontal Integral Float. Example: 1972-1974 MGB.
43:
made by a British manufacturer of that name or its licensees in various designs spanning most of the twentieth century.
20:
Original design incorporating a leather bellows which was replaced by a piston. This image was published 1908 and 1909
991:
838:
797:
777:
211:
193:
349:
SU carburettors were supplied in several throat sizes in both Imperial (inch) and metric (millimetre) measurement.
74:
928:
757:
178:
117:. In 1936, W. R. Morris sold many of his privately held businesses, including S. U., to his listed company,
601:
318:
232:
224:
849:
289:
To prevent erratic and sudden movements of the piston it is damped by light oil (20W Grade) in a
189:
66:
961:
446:
130:
571:
438:
140:
The S. U. Carburetter Company Limited of 1936 was voluntarily liquidated in December 1994.
8:
418:
82:
77:
could remember his mother sewing the first leather bellows. It would be given on loan to
55:
47:
352:
The carburettor identification is made by letter prefix which indicates the float type:
185:
971:
929:"HIF4 Carburetor - Carburetors - Fuel, Intake & Emissions - MGB | Moss Motors"
536:
531:
465:
461:
434:
78:
51:
834:
793:
773:
753:
639:
Handbook of the Collections illustrating Land Transport, II. Mechanical Road Vehicles
583:
557:
New Companies Registered. Private Companies. The Automotor Journal, 24 September 1910
255:(usually referred to as a "needle") that fits inside an orifice ("jet") which admits
906:
868:
457:
267:
249:
134:
16:
972:
Classic Motorsports magazine's guide to understanding, tuning and rebuilding SUs
426:
317:
that was originally manufactured with a slide carburettor, and obtain improved
70:
980:
962:
A very comprehensive SU and Stromberg Carb Needle Selection and Analysis Tool
490:
480:
410:
376:"HV" (1929), "OM" and "KIF" types also exist but were less commonly employed.
143:
In 1996, the name and rights were acquired by Burlen Fuel Systems Limited of
118:
110:
506:
241:
98:
73:
in London in 1899. He helped Herbert to develop the carburettor. Herbert's
498:
494:
484:
442:
430:
305:
283:
148:
86:
40:
450:
314:
114:
493:
also built carburettors based on the SU design which were used on the
403:
398:
144:
941:
475:
S.U. carburetors remained on production cars through to 1994 in the
196:. Statements consisting only of original research should be removed.
519:
414:
260:
468:
type rather than the firm's patented constant-depression design.
46:
The S.U. Carburetter Company Limited also manufactured dual-choke
422:
345:
Three 2-inch SU HD8 carburettors as installed on an E-type Jaguar
290:
286:
size") much less critical than with a fixed-venturi carburettor.
693:
3257 G H Skinner, Carburetting apparatus. reported in page 152,
333:
502:
341:
245:
29:
472:
until the Keihin Constant Velocity carb became stock in 1990.
957:
Burlen Fuel Systems - manufacturer of genuine SU carburetters
337:
An SU fitted to an MZ in place of the original BVF slide carb
309:
301:
956:
476:
256:
24:
409:
S.U. carburettors were widely used not only in Morris's
124:
790:
Malloch's Spitfire: The Story and Restoration of PK350
266:
The flow of air through the venturi creates a reduced
854:
Biographical Memoirs of Fellows of the Royal Society
483:, by which time the company had become part of the
683:The Science Museum's (1965) carburettor, sectioned
978:
464:, but these were of the conventional fixed-jet
967:Guide to setting up and tuning SU carburettors
623:, Wednesday, Jan 06, 1932; pg. 12; Issue 46023
505:Cars. While these appear the same, only their
137:, and traded under the name SU Carburetters.
85:and became a partner in G Wailes & Co of
710:, Tuesday, Jun 02, 1896; pg. 14; Issue 34906
661:, Saturday, Nov 15, 1958, Issue 54309, p.10.
61:
807:
805:
578:, a source licensed under the terms of the
850:Herbert Wakefield Banks Skinner. 1900-1960
882:"SU Carburettor Halted By Protest Strike"
653:
651:
649:
647:
615:
613:
212:Learn how and when to remove this message
825:
823:
802:
402:An HV type carburettor fitted to a 1930
397:
340:
332:
321:and more tractable low-speed behaviour.
231:
223:
92:
23:
15:
811:
719:Skinner-Union Carburettor Improvement.
641:, Science Museum South Kensington, 1936
328:
979:
864:
862:
644:
610:
453:, for much of the twentieth century.
157:
820:
744:
742:
125:The S. U. Carburetter Company Limited
726:
669:
667:
633:
631:
629:
460:including the early versions of the
456:S.U. also produced carburettors for
161:
133:. The companybecame a subsidiary of
101:, in North London. Sales were slow.
859:
732:Profile Professor Herbert Skinner,
417:products but such British makes as
240:SU carburettors feature a variable
13:
739:
28:A pair of SU carburettors from an
14:
1003:
950:
816:. Salisbury: Burlen Fuel Systems.
664:
626:
574:, this article uses content from
987:Constant-depression carburettors
814:SU Carburettor Company catalogue
657:Obituary. Mr. Thomas C. Skinner
512:
166:
935:
921:
912:
900:
874:
843:
782:
762:
549:
393:
713:
700:
687:
676:
595:
580:GNU Free Documentation License
1:
619:Obituary. Mr. G. H. Skinner.
564:
522:to operate a diaphragm pump.
248:. This piston has a tapered,
50:for aero-engines such as the
325:using its accelerator pump.
7:
607:magazine, p 577, 7 May 1954
525:
192:the claims made and adding
10:
1008:
833:, Stratus, Cornwall, 2001
39:was a constant-depression
752:, Stratus, Cornwall 2001
62:Invention and development
992:Carburetor manufacturers
542:
909:company number 03285338
871:company number 00318520
723:, 24 August 1920, p.28.
706:'Lilley & Skinner,
584:"PowerPedia:Carburetor"
812:Burnett, John (2012).
406:
346:
338:
237:
229:
32:
21:
509:are interchangeable.
401:
344:
336:
235:
227:
131:Nuffield Organisation
93:S. U. Company Limited
27:
19:
886:Honest John Classics
721:The Commercial Motor
329:SU carburettor types
83:Lilley & Skinner
71:Farman Automobile Co
48:updraft carburettors
236:HS6 without dashpot
158:Operating principle
56:Rolls-Royce Griffon
942:SU technical pages
770:Tuning for Economy
537:Zenith carburettor
532:Amal (carburettor)
462:Rolls-Royce Merlin
407:
347:
339:
238:
230:
177:possibly contains
79:The Science Museum
52:Rolls-Royce Merlin
33:
22:
831:Wheels to Fortune
750:Wheels to Fortune
734:The New Scientist
695:AutoMotor Journal
222:
221:
214:
179:original research
999:
944:
939:
933:
932:
925:
919:
916:
910:
904:
898:
897:
895:
893:
888:. 5 January 1973
878:
872:
866:
857:
847:
841:
827:
818:
817:
809:
800:
792:, Casemate 2014
786:
780:
772:, Springer 1981
768:Colin Campbell,
766:
760:
746:
737:
736:14 November 1957
730:
724:
717:
711:
704:
698:
691:
685:
680:
674:
671:
662:
655:
642:
635:
624:
617:
608:
599:
558:
553:
458:aircraft engines
244:controlled by a
217:
210:
206:
203:
197:
194:inline citations
170:
169:
162:
1007:
1006:
1002:
1001:
1000:
998:
997:
996:
977:
976:
953:
948:
947:
940:
936:
927:
926:
922:
917:
913:
907:Companies House
905:
901:
891:
889:
880:
879:
875:
869:Companies House
867:
860:
848:
844:
828:
821:
810:
803:
787:
783:
767:
763:
747:
740:
731:
727:
718:
714:
705:
701:
697:3 February 1906
692:
688:
681:
677:
672:
665:
656:
645:
636:
627:
618:
611:
600:
596:
590:
567:
562:
561:
556:
554:
550:
545:
528:
515:
396:
331:
268:static pressure
218:
207:
201:
198:
183:
171:
167:
160:
135:British Leyland
127:
95:
67:Herbert Skinner
64:
12:
11:
5:
1005:
995:
994:
989:
975:
974:
969:
964:
959:
952:
951:External links
949:
946:
945:
934:
920:
911:
899:
873:
858:
842:
829:James Leasor,
819:
801:
781:
761:
748:James Leasor,
738:
725:
712:
699:
686:
675:
663:
643:
625:
609:
593:
592:
566:
563:
560:
559:
547:
546:
544:
541:
540:
539:
534:
527:
524:
514:
511:
449:, and Swedish
395:
392:
378:
377:
373:
372:
368:
367:
363:
362:
358:
357:
330:
327:
220:
219:
174:
172:
165:
159:
156:
126:
123:
94:
91:
63:
60:
37:SU carburettor
9:
6:
4:
3:
2:
1004:
993:
990:
988:
985:
984:
982:
973:
970:
968:
965:
963:
960:
958:
955:
954:
943:
938:
930:
924:
915:
908:
903:
887:
883:
877:
870:
865:
863:
855:
851:
846:
840:
839:0-7551-0047-6
836:
832:
826:
824:
815:
808:
806:
799:
798:9781612002521
795:
791:
788:Nick Meikle,
785:
779:
778:9780412234903
775:
771:
765:
759:
755:
751:
745:
743:
735:
729:
722:
716:
709:
703:
696:
690:
684:
679:
670:
668:
660:
654:
652:
650:
648:
640:
637:E A Forward,
634:
632:
630:
622:
616:
614:
606:
603:
598:
594:
591:
588:
587:
585:
581:
575:
573:
552:
548:
538:
535:
533:
530:
529:
523:
521:
513:SU fuel pumps
510:
508:
504:
500:
496:
492:
488:
486:
482:
478:
473:
469:
467:
463:
459:
454:
452:
448:
444:
440:
436:
432:
428:
424:
420:
416:
412:
405:
400:
391:
388:
384:
381:
375:
374:
370:
369:
365:
364:
360:
359:
355:
354:
353:
350:
343:
335:
326:
322:
320:
316:
311:
307:
303:
298:
294:
292:
287:
285:
280:
276:
272:
269:
264:
262:
258:
254:
251:
247:
243:
234:
226:
216:
213:
205:
195:
191:
187:
181:
180:
175:This section
173:
164:
163:
155:
152:
150:
146:
141:
138:
136:
132:
122:
120:
119:Morris Motors
116:
112:
111:Adderley Park
108:
102:
100:
90:
88:
84:
80:
76:
72:
68:
59:
57:
53:
49:
44:
42:
38:
31:
26:
18:
937:
923:
914:
902:
890:. Retrieved
885:
876:
853:
845:
830:
813:
789:
784:
769:
764:
749:
733:
728:
720:
715:
707:
702:
694:
689:
678:
658:
638:
620:
604:
597:
589:
577:
569:
568:
551:
516:
489:
474:
470:
455:
408:
394:Applications
389:
385:
382:
379:
351:
348:
323:
319:fuel economy
299:
295:
288:
281:
277:
273:
265:
253:metering rod
252:
239:
208:
202:January 2015
199:
176:
153:
142:
139:
128:
107:W. R. Morris
103:
99:Kentish Town
96:
65:
45:
36:
34:
499:Datsun 260Z
495:Datsun 240Z
485:Rover Group
419:Rolls-Royce
306:motorcycles
154:Relocating
149:classic car
87:Euston Road
41:carburettor
981:Categories
892:7 February
758:0755100476
602:The Two Rs
565:References
501:and other
228:HS6 damper
186:improve it
115:Birmingham
852:H Jones,
708:The Times
659:The Times
621:The Times
572:this edit
466:updraught
404:MG M-type
190:verifying
145:Salisbury
526:See also
520:solenoid
479:and the
310:Japanese
151:market.
576:PESWiki
507:needles
491:Hitachi
481:Maestro
447:Triumph
423:Bentley
291:dashpot
250:conical
242:venturi
184:Please
837:
796:
776:
756:
605:Flight
570:As of
503:Datsun
445:, and
443:Jaguar
439:Austin
435:Turner
411:Morris
246:piston
543:Notes
451:Volvo
431:Riley
427:Rover
302:screw
284:choke
894:2021
856:1960
835:ISBN
794:ISBN
774:ISBN
754:ISBN
477:Mini
413:and
315:bike
261:fuel
257:fuel
54:and
35:The
188:by
75:son
30:MGB
983::
884:.
861:^
822:^
804:^
741:^
666:^
646:^
628:^
612:^
497:,
487:.
441:,
437:,
433:,
429:,
425:,
421:,
415:MG
121:.
113:,
58:.
931:.
896:.
586:.
215:)
209:(
204:)
200:(
182:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
.jpg)
.jpg)