Ken,
These are my notes from an APT dyno session a couple of years ago:
>>>
According to the dyno-tuners, Advanced Performance Technology.
http://www.aptfast.com/
.this is what we learned at a session there: the spring issue is
counter-intuitive. According to APT, the going next step heavier spring will
often make an improvement in drivability. It will make the carb richer
throughout the range by increasing the air velocity past the jet. This has
more effect than raising the needle. Heavier damper oil will have the effect
of richening the mixture on acceleration as it retards the rise of the
piston while ultimately having no effect at cruise.
Together the two of them constitute the "accelerator pump" on the SU.
At the session, we observed this on my friend Peter Roses' 29D 100-6 by
swapping springs then making runs on the back streets in Riverside adjacent
to APT. One step heavier resulted in improved performance. Two steps heavier
not so good. Back to the original then settling on one-step heavier.
I've observed the heavier-oil richening. Both of us are running K&N air-fuel
meters so we can see the leanness and richness on the gauges for each carb.
<<<
PS - APT said that some racers were using gear oil in their dashpots.
--
Steve Gerow
Altadena, CA, USA
BN6 - 29D engine, HD8s, Kirk headers
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