> >I have always thought that SU's were measured
> in eighths of an inch.
This is the accepted, official answer.
> Well, maybe I shouldn't have made such a blanket statement without checking a
> whole bunch of carbs. Let me humbly back off and just offer some data points.
>
> 1) I measured an SU model H6, which was 1-1/2" throat diameter
Where did you get this "H6?" The HS4s on my MGB are 1.5" across.
The H6s on my Volvo 122S are 1/4" bigger. Come to my house and
I'll show you. I know this because I tried to fit the MGB backplate
to the Volvo's carbs and they don't fit.
I suspect that this alleged H6 is no such thing. Where did you get
it and what did it come from?
> 2) A friend of mine has SU model HD8's, which are 2" throat, or eight fourths
> of an inch.
They're also 8/8 of an inch larger than 1". Check an H2 or HS2 on a
Spridget, which are of course 2/8" greater than 1" or 1.25".
> 3) The Zenith-Stromberg CD-175 carbs on my XJ12 are 1.75" throat
And my Magnalite Professional Series 8" saute pan is 8" across,
which has just as much to do with SU carbs as the Z-S size. :-)
(Let's not get into OTHER measurements, puh-LEEZE...:-)
> Anybody have any smaller carbs and can supply other data points?
Bugeyes originally came, if memory serves, with H1 carbs of 1-1/8"
throat diameter. These were later upgraded to HS2 carbs, though
I can't recall when -- when the 948 was upgraded from 46 bhp to 48.5,
or when the 1089 was introduced.
Here is the official, factory designation of SU carburetors between
the H1 of the original Bugeye Sprite and the H[D]8 of Jaguars and
some Austin-Healeys. I have personally seen and inspected (though
never measured with calipers) all of the following varieties of
carburetor.
H1 = 1-1/8"
H2 = 1-2/8" = 1-1/4"
H4 = 1-4/8" = 1-1/2"
H6 = 1-6/8" = 1-3/4"
H8 = 1-8/8" = 2"
Between the H and the digit there might be an S or a D. The S,
according to one of my references, stands for "semi-downdraught,"
and points to the fact that the carburetor is actually slightly
inclined from the horizontal. The D on the HD8s mentioned above
refers to a diaphragm used in the dashpot.
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