On Sat, 08 Sep 2007 10:30:23 +0100, "Dave Plowman (News)"
wrote:
The snag with the DCOE Webers and similar designs is the poor atomisation
at low flow rates - ie low engine speeds. It can also be near impossible
to get smooth progression. The SU alters the venturie size to keep
relative airflow speed high to aid atomisation. The downside of this is
you can't make such a clear flow path at maximum power. But for road cars
it's a good compromise. Other ways of course are twin choke designs with a
small and large venturie - but these aren't known for long reliable
service life. Other thing with fixed jet carb is there is no compensation
for the inevitable wear - an SU unless bodged or neglected can be adjusted
as needed.
Can't remember how the provenance between the two companies worked,
but the Dell'Orto version of the Weber side draft carb seemed to do a
better job of low speed pickup.
I remember following some mods I found in Cars and Car Conversions on
an SU carb, and it really could be made to flow very well with some
strategic use of a small grinder. You just had to be careful not to
mess with the flat part of the venturi bridge, or the calibration was
screwed for good and all. A friend of mine had an Imp Sport with an
SU, and that worked best with no spring - just gravity. I suspect it
was hitting full throttle at very low airflow and actually not working
well at all; entirely inappropriate setup.
BTW, venturi doesn't have an "e" on the end.
d
--
Pearce Consulting
http://www.pearce.uk.com