Maintenance and Rebuild of SU Carburettors

There is a wealth of information about SU carburettors on the web because they were so widely used for a long time. I considered writing a full-scale article about maintenance and rebuild but I decided that it would not only be repeating the contents of the Workshop Manual, which was never the intention of this site, but I would also be reinventing the wheel as far as web articles are concerned. I therefore propose to use this page to record all the best web resources about our carbs that I can find and I'll leave you to decide which suits you best: Click each description to open that page. I will add more as I find them.

The only part of a rebuild that might be challenging for the amateur owner is the repair of loose throttle spindles. This involves using an in-line reamer to open out the spindle holes so as to insert repair bushes. The reaming has to be straight and accurate and the tool is expensive for one-off use, so you might want to farm this bit out to a machine shop. If your spindles are still tight then you don't have the problem, so check this point early on. If the engine is running before you start the work, you can test for wear by spraying WD40 onto the outside of the spindle hole. If the engine note changes, you have wear that is allowing air in behind the butterfly valve (= carbs that are impossible to tune accurately).  Before ordering any parts, please read the separate article about ethanol fuels, because it may affect your choice of parts and you need to check with suppliers whether their parts can cope with E10 fuel.

Please note that if you are reading this because you think your carbs are causing tuning problems but there are no obvious leaks or overflows, do tackle everything else BEFORE you touch your carbs e.g. ignition, timing, valve clearance (see Dana Britton's website below).  Most carb problems are electrical! if you are stripping them down as part of a complete rebuild or engine overhaul, then read on:

The primary source of all things SU is now Burlen Fuel Systems in Salisbury, UK. This company worked closely with SU and is now the manufacturer of all SU parts. (SU was bought by William Morris in 1926 and remained in BMC and its successors until 1988, when it was bought by an American conglomerate. After more changes of owner, and when all new cars had fuel injection, Burlen negotiated the purchase of the intellectual property and the trade-mark so that the classic car market is still well served).The Burlen SU website contains on-line instructions for maintenance and rebuild, FAQs, a parts e-shop, histories, application searches and pretty much all you will need. If you decide that a rebuild is beyond your abilities, they will do it for you. If you get stuck on something, ring them up and they're very helpful.

Quite a few specialists and enthusiasts have also contributed their guidance and tips and it's worth looking at these before you start:

MGA Guru (Barney Gaylord) This link takes you to his index for Carb-related articles. CB210 is the first of the series dealing with rebuild.

SU Carburettor Tips by Jim Taylor (Jaguar Clubs of North America)

Care & Feeding of SU H4 Carburettors (Jim in NH's Blog)

SU H4 Carburettor Tuning (MG Experience Tech Library)

Tech Tips by Dana Britton (trades in Wichita, Kansas)

WinSU Software download ( A Windows application that helps you decide the best SU needle for your car, but this is only relevant if you have carried out major modifications and, if you have, then a test run on a dynamometer is an alternative solution).


John Twist of University Motors has recorded a series of helpful videos. Click HERE to see the first one, then use the Youtube navigation menu (on the right-hand edge of their page) to find the others.

SCCR Services have also produced a hands-on demonstration video HERE. You can skip the ad at the outset. See the Youtube menu for their other clips.


"Series A and Magnette Tuning and Maintenance" by Philip H Smith - A "must-have" for the Magnette owner published by G T Foulis in 1957 (but there were at least two revisions. My 3rd Revision copy is dated 1961). Out of print but I found copies for sale on line without any difficulty.

"Tuning SU Carburetters"- published in 1968 by Speed Sport Motor Books. It is long since out of print but you may find one via specialist book dealers or on web auction sites. You can read it on-line HERE.

There is a Haynes manual for SU carburettors but it seems to be out of print with the publisher. However, I found it on Amazon and no doubt specialist motor book shops could come up with it.


All the specialists will have the routine maintenance parts but you can go direct to the source that they probably use: Burlen Fuel Systems (see above).


#1 Trevor Jones 2015-01-27 18:10
Well done Malcolm, this is idiot proof as you have gathered all the good stuff in one place, it interesting that most of the information comes from the US.
Thank you for your efforts, I need to do my carbs I will order my parts from Burlen this week. Brilliant Trevor Jones

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