James Fuerstenberg scribed:
Subject: valves and ZS damper oil
> Re: easy valve adjustment.
> re eric f.'s question re ZS carbs and damper oil. Neither I nor anyone I
> know who race with SUs use damper oil. just a little WD40 on the piston and
> metal to metal surfaces. the piston comes up faster and gives better
> throttle response.
Buzzz! Note that this is a RACE modification- some racers even remove the
dashpot damper altogether. This is fine on the track where you are
running full throttle most of the time, but will be hell on smoothness and
low end response on the street.
> If you must use oil, marvel mystery oil, ATF or genuine
> SU or AZ damper oil (which I have seen) would probably work fine.
Yes, you must. (on the street). This is important. Sometimes even 20/50
if you get too much carb flutter for some reason.
Why do SU's need piston damping? There's one major reason:
SU's are all around good, simple, and reliable carbs. There is one
drawback with the basic SU design -response time when you hit the throttle.
If the piston rises to fast, the gas can't keep up with the increase in
air flow, and the mixture will go lean and loose power. (This is because it's
a lot easier to suddenly move the air faster than the fuel) Damping the action
of the piston keeps the *air response* in sync with the *fuel response* when
you step on it suddenly, thus keeping the mixture correct (at the cost of
delaying the overall response time).
This is about the only real advantage a Weber's, et. al., have
over SU's, in design. They have an accellerator pump, which lets you open
the air fast AND provide the extra squirt of fuel needed during the transition.
It's very easy for an SU to have the same (or better) flow (and the resultant
power) as a different sidedraft carb of the same size, *during constant
and "slowly changing" flow states*. (and certainly better flow than a
downdraft design.)
This is rarely an issue on the street, and not even much of an issue
in many competitions, except where there's a lot of fast throttle
transitions. SU's are usually easier and cheaper to tune for smooth,
economical street use, and many competition setup's as well.
________
/___ _ \ Roger Garnett (Roger_Garnett@cornell.edu)
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