The vacuum advance is shot but that is not the source of your stumble. That
is the classic symptom of being a little lean. Richen up your carbs a
little. If you have SUs then about a quarter to half turn on the mixture knob
on the bottom. If Solex then one step smaller air or one step bigger main.
Try the air first.
The vacuum advance has been around a lot longer than emission concerns. It
is a performance item and the car will run better with it working.
keithw
In a message dated 6/12/2013 8:11:22 P.M. Pacific Daylight Time,
graemes@internode.on.net writes:
First up, the vacuum advance is an emissions device.
You can safely
remove theB vacuum source and test drive the car.
It only does its thing on
cruise or trailing throttle, it does not
contribute to engine power.
The
only caveat is you must BLOCK OFF the vacuum hose to prevent the
engine from
sucking in air when the vacuum port is exposed in the
carb. throttle.
For
sure the vacuum advance mechanism in the distributor does
eventually gum up so
badly it is no longer operative.
Providing the plates inside the mechanism
are not pitted and
groovedB by the tiny ball bearings, it should be reasonably
easy to
clean and re-lube so it all functions smoothly.
The vacuum actuator
is a different kettle of fish.
If the arm doesn't operate when subjected to
vacuum it is schtuffed,
non-repairable.
Once the diaphragm is holed or
perished, game over.
Suction by the human should be enough but a little
vacuum pump is
handy to see that things do operate correctly and more
importantly,
stay operated.
i.e. with a constant source of vacuum, the
mechanism should stay
put,B not slowly return to normal, that indicates a
vacuum leak
somewhere.
Let me know if you need any pics. and I'll email them
to you
directly.
Regards, Graeme S.
----- Original Message -----
From:
"wattaj" @yahoo.com>
To:"Roadster List"
Cc:
Sent:Wed, 12 Jun 2013 19:45:58
-0700 (PDT)
Subject:[Roadsters] Vacuum Advance Issue?
Hello,
I have an
issue where at a steady highway cruise speed, just around
3000 RPM or higher,
I get regular hiccups, sputtering, etc.. If I
drop below
3000 RPM I am
usually fine. The engine will pull strong all the way
up to
where I dare
accelerate. I have always been suspicious of my
distributors
vacuum advance.
Popping of the distributor cap, I tried to manually
move the
advance it by
sucking on the tube, but it would not budge. I took the
advance
mechanism off
the distributor and it was frozen stiff. After some
serious
pushing I got it
to move manually, but would still not move under
suction. It
looks like I
should replace the vacuum advance unit. I am curious if
that
might be the
cause of my cruise speed issues? Thanks in advance (no
pun
intended) for the
help.
Cheers,
Alan
Tualatin, OR
67-1600
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