You are right Jon, this is like trying to decide what oil is best for your
engine, and EVERYONE has an opinion! I like to use ATF in the cooler
months.. It seems to give faster response. In the summer motor oil may be
best. The whole theory behind SUs is to give you a variable venturi... On
the 2L race car when the rules required SUs for D Production we ran nothing
in them at all. This made them cough a sneeze at slow speeds, but so did the
race cam... But oh the throttle response at 4800 and above (we wound it to
7800) The Solex carbs and cam have a reputation for being less drivable on
the street, because there is too much carburetor for that size engine until
you get the RPM up. When you have a large bore carb on a car and mash the
throttle open you get a huge drop in induction system vacuum. This almost
completely stops the carburetor from drawing fuel into the air stream, hence
they have accelerator pumps to squirt extra fuel into the airstream until
the engine speed picks up and the system starts running normal again. With
SU carbs there is no accelerator pump. When you mash the throttle the slides
that are dampened by the oil essentially varies the size of the carburetor
keeping the system drawing air and fuel at a more constant velocity. On the
race car we had enough compression and we wound the engine high enough that
the solex carbs gave better drivability.
So.... If when you mash in the throttle at a fairly slow speed and the car
falls on it's face a little, try a thicker oil. If it just takes off and
screams.. you might get quicker response with thinner oil.... just my humble
opinion and no scientific experience!
Gregg
'70 1600
McMinnville, OR
-----Original Message-----
From: owner-datsun-roadsters@autox.team.net
[mailto:owner-datsun-roadsters@autox.team.net]On Behalf Of Jon Wissler
Sent: Sunday, March 19, 2000 08:40 AM
To: datsun-roadsters@autox.team.net
Subject: SU Carb Oil Question
Here is another classic neophyte (aka stupid) question concerning
which oil to use in SU carbs. I have told to use 10W, 30W, and ATF from
various sources. What does this learned list have to say on the subject,
and are there different conditions to warrant the use of different fluids.
Thanks in advance for the advice.
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