>
> I saw references to "light damping" and "heavy damping" for carbs. Which is
> the preferred way, and what are the advantages/disadvantages to each. I am
> referring to using either Marvel Mystery oil or 30w in the dashpots.
>
> Thanks,
> Dave
>
There are various themes on what kind of damper oil to use for which kind of
performance. One hears such things as Marvel Mystery Oil, ATF, to multi-
viscosity motor oil. Obviously, the heavier the oil, the slower the piston
rise and the greater the accelerator enrichment (but too slow a rise time will
"throttle" the air flow and reduce response). Too light an oil can allow too
quick piston rise with a characteristic lean stumble and insufficient damping
to reduce slow speed vibration.
With regard to Zenith-Strombergs, excessive or consistent oil loss from the
damper indicates a defective o-ring on the needle adjusting screw. This allows
the oil to leak out around the needle into the engine. While these o-rings
and screws are available, the are retained by a unidirectional star clip that
can be a real bear to get out without having the clip score the bore of the
guide tube (which can cause friction with the damper). The best way is to
fashion a slender hook from one of the fiendish looking dental picks available
in surplus stores and reach down the bore tube and try to hook it in the center,
thus reversing its preload by bending it upwards. Alternately, you can remove
the needle and gently tap the screen from below with a suitable soft drift. If
the star clip's pressure is not too great, it should come out without too much
damage to the bore.
Zenith Lube Oil comes in a handy size dispenser can for easy filling (no more
oil spills on the carbs trying to pour from a quart can) and tool box stowage.
I understand that for the Zenith-Strombergs that I'm using the viscosity and
chemistry the engineers designed the carb around, which is I believe something
like 20W (I don't really know about the chemistry) - but I get a warm feeling
anyway! Its always best to check with the carb manufacturer manual to find
out what they recommend, rather than take your chances otherwise.
As for the Zenith-Strombergs, last year I had a situation which occured during
winter stowage for my '79 Lotus 'eclat. It seems that I was getting a gas leak
thru one of the vent holes at the top of my rear carb. The gas was leaking
onto the starter motor. Deciding to investigate, I took off the air box front
cover, and was able to plainly see where the leak was coming from. What to do?
Instead of hitting the panic button and overhauling the carbs before I tried
to do anything, I wondered whether the problem was due to a stuck float - it
certainly seemed plausible! Ok, so at that point I decided to look to see if
the dashpots were topped off - No they weren't! I then said to myself, even
though at the time I didn't think it would correct the problem - I really
thought that I would need to do an overhaul to unstick the float - Let's just
see what happens if first I top off the dashpots? In no time at all, the
problem disappeared and did not reoccur with regular attention to the dashpots.
BTW, Zenith-Strombergs are a lousy performance carb, no fun to work on, and
quick to lose their tune. As an emission carb they aren't much either. So,
as I write this, I'm pleased to say that I've decided to make the switch to
Dellortos which are just a clone of Webers. I am planning on using mercury
carb stix (used for motorcycle carb syncing) to adjust them, in addition to
a ColorTune kit that I purchased last year.
-- Tom Watt
Open Software Foundation
11 Cambridge Center
Cambridge, MA 02142
(617) 621-8711
InterNet: watt@osf.org
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