Talk:SU carburetor
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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.
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" ----------------------------
[edit] 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)
