Talk:SU carburetor

The vacuum acts on a flexible rubber membrane connected to the piston. The carburetor, and with it the engine, will no longer work if the membrane develops a leak, and the piston can no longer move up.

Disputed info: The piston is machined to a close tolerance fit to the dashpot housing. No rubber diaphragm is fitted to an SU, only similar Strombergs and Pierburgs.

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Also...this page probably needs to explain a bit more how these carbs work and their differences between traditional carbs....something like:

The main problem with traditional carbs is they are trying to use pressure differences to mix a liquid (gasoline) and a gas (air). Air compresses/decompresses with changes in pressure, and thus its' density changes as well. Liquids (gasoline) do not experience any significant density change with these pressure changes; thus as more air is drawn through a fixed venturi, it's pressure drops and there is "less of it" than the pressure drop would suggest.

The upshot of this is that a simple single venturi carb tends to go rich as more air goes through it. Multiple circuits, emulsion tubes (which bubble air through the fuel in an attempt to get it's density to change with the pressure drop) are their solution at minimizing the problem. The SU carb gets around this problem with its variable venturi design; as more air passes through the venturi, the venturi size is increased such that the air velocity (and corresponding pressure drop) is constant. This is why SU carbs are sometimes termed as "CV" (constant velocity) or "CD" (constant depression, a british term for pressure drop??) carbs.

We also could tie in here how now that the pressure drop is constant, the variable sized jet (needle/seat) takes care of the fuel/load problems.

Of course the language/presentation of these ideas need cleaning up!

--Ken R. Dye "used to race a datsun 510" ----------------------------

Spelling of carb

There are several ways to spell carburetor/carburettor/carburetter. The second two are listed in UK dictionaries, the first is American I believe. This article moved from one spelling to another and another. For the sake of consistemcy within the article, I have made the spelling 'carburettor' throughout. I chose this because it is the most usual of the UK spellings, and because it was a British company. I have not changed the spelling in the article name. Emeraude 17:21, 8 December 2006 (UTC)

The spelling of "carburettor" in this article should be spelt "Carburetter" as this is how the SU Carburetter Company spell it. This artlce is about this compnay and should there fore use the same spelling as that of the corporate web site. —Preceding unsigned comment added by Burlenwiki (talk • contribs)

Poor Atomization

My direct experience on the SU Carbs, using more advanced diagnostic equipment, is that Atomization was not as it was claimed to be. At idle, or at constant speeds, atomization of the mixture was incomplete. The "downstream" side of the needle often acted as a capillary, allowed a path for unevaporated fuel, which would collect and then "break off" as solid fuel droplets or chunks, into the airstream. This is why idle speeds on many SU equipped cars would often hiccup, as the engine on one or two cylinders would suddenly have to burn through this stuff.

-- John F. -- former garage owner —Preceding unsigned comment added by Johnfalky (talk • contribs) 19:44, 21 June 2009 (UTC)

Piston Lubrication

For CV carburetors to operate correctly the pistons and slides need to be lubricated for very low friction. My experience with these carburetors leads me to believe that the factory lubrication of the pistons and slides was powered graphite. Powered graphite is also used for lubricating the piston in toy stirling engines where very low friction is required. I do not know if this is the ideal lubricant but it seems to work quite well. Arydberg (talk) 12:55, 27 July 2009 (UTC)

"pistons and slides need to be lubricated"

Slides (i.e. the central tube of the piston) are lubricated by the dashpot oil. The piston doesn't contact the chamber walls, so there's no friction. If your pistons are contacting (a common problem) then they're likely oversized owing to a build up of corrosion on the aluminium. The fix is to polish this off, not lubricate it. Aluminium corrosion is harder than aluminium and mixed with an oily lubricant it makes a powerful grinding paste that will wear the chamber walls out. Andy Dingley (talk) 13:08, 27 July 2009 (UTC)

Copyright violations

The entire History section of this article, as well as SU Carburetter are taken from the SU Carburetter Company corporate site. The text was added on November 6, 2009 but User:Burlenwiki. I will add both this site and SU Caruretter to Wikipedia:Copyright problems/2010 May 19 Scottanon (talk) 19:49, 19 May 2010 (UTC)

That's not a copyvio, it's a WP:COI if anything (look who Burlen Fuel Systems are) Andy Dingley (talk) 20:20, 19 May 2010 (UTC)