[v12-engine] Should Pre-HE Advance Capsule Hold Vacuum?

My E-Type was recently converted to EFI. The car now starts and
runs quite well, except for running much hotter than it did pre-
conversion. One possible cause may be the prescribed pre-HE
distributor advance capsule (AAU6704) installed as part of the
conversion. It will not hold a vacuum. A low pressure bubble test
shows that air will seep from the hose connection side, through the
diaphragm into the opening for the actuator arm. It is difficult
to get any actuator movement at all when drawing suction by mouth.
Is this normal for this particular vacuum capsule?

Also, the advance capsule is connected directly to the rear port on
top of the right throttle body. It has a larger bore, and is more
centrally located over the disc than the front port is. At idle,
there is no detectable vacuum. Am I connected to the correct port?

Since the conversion, I have taken about 24 specific actions and
spent about half the cost of the conversion in attempts to control
the heat. The list of possible causes has to be getting shorter.

Thanks for any assistance!–
Don Snyder, '59 XK-150 DHC, '73 E-Type 2+2
San Antonio, Tx., United States
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In reply to a message from Don Snyder sent Sat 22 Sep 2012:

HI, Don,on my 78 V12,i run a lot of advance(around
40*),also just to cool my engine in this Texas weather, I
had to add a big and small eletric fans!

on my vacuum advance unit, I attach hose to the TB that
closes it off at idle,(retards timing,engines have a
tendency to idle rough with lot of advance), as soon as T
plate opens advance increases for cruising response and good
MPG,mine around 18mpg 60-70mph.

I like to run all the timing the engine can handle without
hard starting when hot!

my comp ratio 9-1 pistons, pre-he.

but the two fans cured my overheat problems.–
The original message included these comments:

runs quite well, except for running much hotter than it did pre-
conversion. One possible cause may be the prescribed pre-HE
Also, the advance capsule is connected directly to the rear port on
top of the right throttle body. It has a larger bore, and is more
centrally located over the disc than the front port is. At idle,
there is no detectable vacuum. Am I connected to the correct port?
spent about half the cost of the conversion in attempts to control
the heat. The list of possible causes has to be getting shorter.
Don Snyder, '59 XK-150 DHC, '73 E-Type 2+2
San Antonio, Tx., United States


Ronbros
daytona fl. / Austin TX., United States
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In reply to a message from Don Snyder sent Sat 22 Sep 2012:

The vac advance capsule is supposed to be leak tight.

Alex P–
alex paterson
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In reply to a message from Don Snyder sent Sat 22 Sep 2012:

The vac advance capsule is supposed to be leak tight.

On a pre-H.E., I believe that’s true. It’s not true on the H.E.,
though, which has an orifice leak necessary to allow the vacuum
regulator to work right. So there’s always the possibility that your
car somehow got an H.E. vacuum advance module somehow.

In my experience, here’s how to tell: If you put your mouth on a
hose connected to the module and suck and can pull the advance in,
it’s OK, even if there’s a tiny hiss due to an orifice leak. If you
suck and just get a free flow of air, no movement, the module is
toast. If you try to move the actuator rod in and out by hand and
get stiffness followed by a crunching sound, it’s toast.

– Kirbert

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !On 23 Sep 2012 at 10:23, alex paterson wrote:

In reply to a message from Kirbert sent Sun 23 Sep 2012:

Thanks to all who have responded. I needed a sanity check because
I have now purchased two brand new pre-HE vacuum units from two
different vendors; and both were leakers. Both were the AAU6704
units with 6-10-8 stamped on them, and both would barely twitch (no
longitudinal motion) with mouth suction. In contrast, two old HE
vacuum units in my possession definitely have good longitudinal
motion, and both are air tight. So my quest for a leak tight pre-
HE unit continues.–
The original message included these comments:

On 23 Sep 2012 at 10:23, alex paterson wrote:

The vac advance capsule is supposed to be leak tight.
On a pre-H.E., I believe that’s true. It’s not true on the H.E.,
though, which has an orifice leak necessary to allow the vacuum
regulator to work right. So there’s always the possibility that your
In my experience, here’s how to tell: If you put your mouth on a
hose connected to the module and suck and can pull the advance in,
it’s OK, even if there’s a tiny hiss due to an orifice leak. If you
suck and just get a free flow of air, no movement, the module is
toast. If you try to move the actuator rod in and out by hand and


Don Snyder, '59 XK-150 DHC, '73 E-Type 2+2
San Antonio, Tx., United States
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Thanks to all who have responded. I needed a sanity check because I
have now purchased two brand new pre-HE vacuum units from two
different vendors; and both were leakers. Both were the AAU6704 units
with 6-10-8 stamped on them…

I think those numbers might indicate the vacuum at which movement
begins, the vacuum at which it’s all in, and the total mm of
movement, or something like that.

and both would barely twitch (no
longitudinal motion) with mouth suction.

Do they all have the vacuum connection on the OPPOSITE side of the
diaphragm from the actuator rod? Because any with the vacuum
connection on the SAME side are vacuum retard actuators.

Could you move the rod in and out with your hand? In an actuator in
good condition, you should be able to move it smoothly and feel the
spring as well as the flexing of the diaphragm. When that diaphragm
has dried out and hardened into a cracker, though, you can feel it
crunch as it cracks when moved.

In contrast, two old HE
vacuum units in my possession definitely have good longitudinal
motion, and both are air tight.

Others have found H.E. units without the air leak. Not sure what’s
up with that, as the vacuum regulator definitely requires an air
leak. It’d be easy enough to add one, of course, by installing a
dedicated orifice in a hose. Or perhaps they figured out how to
build it into the vacuum regulator itself.

– Kirbert

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !On 23 Sep 2012 at 19:40, Don Snyder wrote:

In reply to a message from Kirbert sent Mon 24 Sep 2012:

Thanks to all who have responded. I needed a sanity check
because I

have now purchased two brand new pre-HE vacuum units from two
different vendors; and both were leakers. Both were the AAU6704
units

with 6-10-8 stamped on them…

I think those numbers might indicate the vacuum at which
movement
begins, the vacuum at which it’s all in, and the total mm of
movement, or something like that.

From Roger Bywater�s website, the numbers indicate vacuum at which
movement begins, vacuum at which it�s all in, and maximum degrees
of advance.

and both would barely twitch (no
longitudinal motion) with mouth suction.

Do they all have the vacuum connection on the OPPOSITE side of the
diaphragm from the actuator rod? Because any with the vacuum
connection on the SAME side are vacuum retard actuators.

Yes. All have the hose connection-diaphragm-rod configuration; and
they all look identical except for the number stampings. Direction
of motion with increasing vacuum for all units would be the same.

Could you move the rod in and out with your hand? In an actuator
in
good condition, you should be able to move it smoothly and feel
the
spring as well as the flexing of the diaphragm. When that
diaphragm
has dried out and hardened into a cracker, though, you can feel it
crunch as it cracks when moved.

The rod on the first pre-HE unit could be moved by hand and the
diaphragm appeared to be flexible, as a new one should be. The
second one is currently installed in the distributor, but since it,
too, is �fresh out of the box� new, it should be flexible.–
Don Snyder, '59 XK-150 DHC, '73 E-Type 2+2
San Antonio, Tx., United States
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In reply to a message from Don Snyder sent Mon 24 Sep 2012:

Don, I should add that after having hi-overlap cams my idle
vac dropped, 1995, so checking with Crane Electronics in
Daytona, an R&D rep looked at my advance unit,put a digital
vac test on it. say not good for a performance curve.

suggested I graft a Chevy HEI vac head on the jag base!

GM unit top head has an adjutable screw in center of inlet
port, NICE!, now I can adjust both spring tension and
movement degrees amount,
works great until I went to a standalone EMS, now I can
adjust ALL fueling requirements as well as ALL timing
events, by far the best of both worlds!

gotta LOVE technology, good,bad, or indifferent!!! also
helps with sanity issues,hehe!

Ron–
The original message included these comments:

Thanks to all who have responded. I needed a sanity check
have now purchased two brand new pre-HE vacuum units from two
I think those numbers might indicate the vacuum at which
movement
begins, the vacuum at which it’s all in, and the total mm of
Don Snyder, '59 XK-150 DHC, '73 E-Type 2+2


Ronbros
daytona fl. / Austin TX., United States
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In reply to a message from Ronbros sent Mon 24 Sep 2012:

Ron,

The adjustable vacuum unit is an interesting approach to the
problem. All the issues associated with grafting and proper
adjustments of the GM head are a bit intimidating to me, but the
suggestion does bring to mind possibilities with the HE vacuum
units that I already have on hand. The HE units are designated 5-
15-12 (starts movement at 5 In. Hg., all in at 15 In. Hg., 12
degrees maximum movement). The pre-HE advance unit characteristics
are 6-10-8. It should be fairly simple to attach a clamp to the HE
actuator arm to limit its travel to about 2/3 of its current
movement. That should make it all in at 12 In. Hg., with about 8
degrees of advance (5-12-8). That�s not perfect, but probably much
closer to what it should be than what I have now.

A third new pre-HE advance unit should arrive tomorrow. However,
the clamped HE unit concept does seem to be a possible alternative
solution. Thanks for the input.–
The original message included these comments:

Daytona, an R&D rep looked at my advance unit,put a digital
vac test on it. say not good for a performance curve.
suggested I graft a Chevy HEI vac head on the jag base!
GM unit top head has an adjutable screw in center of inlet
port, NICE!, now I can adjust both spring tension and
movement degrees amount,


Don Snyder, '59 XK-150 DHC, '73 E-Type 2+2
San Antonio, Tx., United States
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In reply to a message from Don Snyder sent Mon 24 Sep 2012:

It should be fairly simple to attach a clamp to the HE
actuator arm to limit its travel to about 2/3 of its current
movement. That should make it all in at 12 In. Hg., with about 8
degrees of advance (5-12-8). That�s not perfect, but probably much
closer to what it should be than what I have now.
A third new pre-HE advance unit should arrive tomorrow. However,
the clamped HE unit concept does seem to be a possible alternative
solution.

Well, the third pre-HE advance unit did not arrive. The
representative told me that stock was depleted, the latest
manufacturer no longer makes the unit, and that a new manufacturer
for the part is being sought. He could not tell me �when� or
even �if� production would begin.

The clamped HE advance unit concept has now become reality. A clip-
on nut was attached to the HE actuator arm to limit travel, and the
unit was installed and tested. While operating temperatures are
still higher than pre EFI conversion levels, they are significantly
better than they were with the leaking pre-HE advance units, so
this may help to keep the car on the road until a proper advance
unit can be acquired.–
Don Snyder, '59 XK-150 DHC, '73 E-Type 2+2
San Antonio, Tx., United States
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In reply to a message from Don Snyder sent Tue 25 Sep 2012:

Hi Don,

This is an other approach…

http://www.jag-lovers.org/snaps/snap_view.php3?id=1305116669

Best
Aristides–
Aristides Balanos, 1986 XJ V12,VDP - www.e-psychi.com/jaguar
Roussillon, Provence, France
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