E-type Series 3 V12 vacuum advance conversion and TVS pipework

[Hannu]

Hi,
I own a 1972 Jaguar E-Type Series 3 V12 2+2, originally a US-specification car. I've owned it since 2000.

The car underwent a partial emissions-system conversion over the years. The original distributor vacuum retard unit was replaced with a vacuum advance unit in 2007. The advance unit is currently connected to manifold vacuum from the vacuum port at the base of the LH rear carburettor. The exhaust bleed pipes had already been removed by a previous owner, and I have recently removed the air cleaner temperature vacuum switches and the gulp valve while tidying up the engine bay and refurbishing the carburettors. The Thermostatic Vacuum Switch (TVS, C37430) and the carburettor bypass valves are still installed.

Question 1
When replacing the original vacuum retard unit with a vacuum advance unit, what is generally considered the best vacuum source for the advance capsule?
• Direct manifold vacuum?
• Ported vacuum from the carburettor throttle edge?
• Some other arrangement?
I would be interested in hearing what other Series 3 V12 owners are using and why.

Question 2
Once the distributor has been converted from vacuum retard to vacuum advance, does the Thermostatic Vacuum Switch (TVS, C37430) still serve any useful purpose in the distributor vacuum circuit?
Would it be reasonable to remove the associated vacuum pipework connected to the TVS ports (C, D, F and T), or is there a good reason to retain the system?

According to the following Jag-Lovers post:
https://forums.jag-lovers.com/t/e-type- ... g/117981/4
C = carburettor
D = distributor
F = filtered air from the RH air cleaner
T = central T-piece connecting the four bypass valvesF and T were not always connected, depending on model year and emissions requirements.

Question 3
Does anyone have a copy of Jaguar Service Information Volume 1, Number 11, Item 113 (March 1973), or know where it can be obtained?

I found the following reference on the E-Type UK forum:
viewtopic.php?t=10020
"From engine no. 7S8444 the Thermostatic Vacuum Switch was deleted from all non-exhaust-emission (E-Type Series 3 V12) engines.""(Source: Jaguar Service Information Vol. 1 No. 11, Item 113, March 1973)"
I would very much like to see the original Jaguar document.

Reference discussions
viewtopic.php?t=15092
viewtopic.php?t=9665
https://forums.jag-lovers.com/t/e-type- ... g/117981/4

Thanks in advance for any advice.

Best regards,
Hannu Savolainen

[lowact]

Re Q1. The best way to connect a vacuum advance distributor is how Jaguar did it, including dump valve and vacuum regulator, here is an explanation: https://forums.jag-lovers.com/t/how-to- ... 4?u=lowact
The only utterly wrong way is as you are doing; bottom throttle-edge trappings are for vac. retard. Vac advance requires a top edge tapping to be retrofitted

[MarekH]

Dear Hannu,
take a look at the US edition of the Owners Manual booklet which is tan coloured (as opposed to the UK spec blue booklet). The US edition contains an extra chapter which explains how all of the emissions equipment works, all of the situations when Jaguar attempted to retard ignition advance. You can also see this better by reference the 1974 Parts Manual which lists all of the vacuum hose routing diagrams. I posted an annotated copy of this on the jag-lovers.org website back in 2007 and you can see it at
https://www.jag-lovers.org/snaps/snap_v ... 1190800376

The airbox temperature sensor and associated hoses you have already removed are an attempt to keep inlet temperature constant by mixing warmer air from by the exhaust manifold with air from the trumpets and altering that mix depending on air temperature in the airbox.

The thermostatic valve is Jaguar's attempt to control where vacuum is routed to depending on coolant temperature. This was used to control distributor retard by temperature and also when bypass valves can be active. See the manual or my annotations for the when and why C, D, T and F connect.

You can look through the archives both here and on j-l for opinions as to how to implement vacuum advance. Briefly, you can consider ported vacuum to be a subset of manifold vacuum. There is no ported vacuum at idle and the rate at which it cuts in or cuts out as throttle opens is more direct than a simple connection to manifold vacuum. Manifold vacuum presents a vacuum signal at idle which will drop away as throttle opens, so ported vacuum will appear to offer a greater ignition advance boost as throttle initially opens, but it runs the engine hotter and more retarded at idle. See Philip Lochner's discussion of the topic on this forum from a few years ago.

Colin confirms what I said on j-l when you asked about connections - you have connected your advance capsule to a port designed for a retard capsule so you have no vacuum signal other than at idle. You need to plug the lower left rear carburettor port and redirect the hose to pick up vacuum from the manifold directly or from a tapping just outside (i.e.airbox side) the top edge of a throttle butterfly.

kind regards
Marek