elementary manifold vacuum question

[Tom Parker]

Greg Hermann <bearbvd at sni.net> wrote:

>>>this manifold just has 2 large 'pipes' which go to each intake port, these
>>>come from a pretty large base which meets up with the downdraft carb. so
>>>there is no balance tube as such. I am measuring this from a port on the
>>>manifold, but come to think of it, this is about 1 inch out of the front
>>>head intake port, so the other port isn't really a major part of this
>>>reading.
>>
>>I've not looked closely at such a downdraft Weber, but I believe it has one
>>big venturi and a smaller one inside that? What I'm trying to say, is that
>>it is basically a single barral feeding both ports via a phlenum (ok, its a
>>clever word for an air box, and I can't spell it) in the manifold.

>It would depend on the carb model, of course, but most of this sort of
>Weber downdrafts are PROGRESSIVE two barrels--a small primary, and a larger
>secondary, which only opens at higher loads. Sort of like the secondaries
>on a Holley four barrel.

Well, I've never looked closely at how either carb works, but I'm under the
impression that when both venturis are open (full throttle or whenever) the
carb act as if it had one venturi.All the air exits the carb in the same
general place at the bottom of the carb, rather than one venturi feeding each
port isolated from the other.

>The two barrel Dellorto on the Mini is like two
>separate one barrel carbs which simply share the float chamber. With it,
>flow to the two intake ports is completely separated, excepf for the goings
>on in the balance tube, if any.

Yup, thats how mine works.

--
Tom Parker - tparker at nznet.gen.nz
           - http://www.geocities.com/MotorCity/Track/8381/