V12 Opus Distributor Vacuum Module Failure

[FRE444K]

<t>I've read most of the posts regarding manifold v ported vacuum take off and the pros and cons of each method. I think i've overloaded on all the information and ended up confusing myself and so I would appreciate some clear advice if that is possible.
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My engine has 4 SU HIF44 carburettors with a ported vacuum point. The distributor is an Opus ignition conversion kit from a well known Jaguar parts supplier and has a retard vacuum module.<br/>
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The issue I have is the vacuum module has failed and so my questions are:<br/>
<br/>
1) Should I replace like for like<br/>
2) Replace with an advance module <br/>
3) or as it runs quite nicely ignore the issue and run it as though there is neither vacuum advance or retard?</t>

Regards

[MarekH]

Vacuum retard and vacuum advance are two totally different things designed for two totally different objectives and take their vacuum source from different places.

Which option and you want to implement it depends on what the objective is. Static and centrifugal advance are then added to make up the full profile.

Believe it or not, there were vacuum capsules in the 1970s which had both advance and retard connections on either side of the diaphragm.

kind regards
Marek

[lowact]

Also all modern (distributorless) ignition systems both advance and retard as appropriate.

If you are happy with how the car performs, including warm-up time and fuel economy, have no Opus issues, can't justify the expense and would like to be as original as possible, then yr option 3. I suspect at least 90% of all early V12s now operate like this. Make sure to block off all vacuum ports on both the manifold and the carb, including to the failed (leaking) distributor vacuum module.
Alternatively, I’ve checked yr posts, photos of yr engine. I think you already know what you really want to do? Options as per this 2021 post of Phil’s on Jag-lovers:
https://forums.jag-lovers.com/t/v12-mod ... ems/403310

If anyone wants an xjs ignition system in good condition, I will shortly be listing one in the Wanted/For Sale sub-forum.

[FRE444K]

Thank you for your responses.
I've decided to leave things as they are and enjoy the car this summer then in the autumn change the vacuum module for an vacuum advance type and go from there. I'm hoping the vacuum advance may improve fuel consumption on part throttle when on the open road.

Regards

[vee12eman]

From a previous post of my own, I found the part number and source of the advance unit I bought: “vacuum advance unit (54405202) recommended by the British Vacuum Unit”. I used ported vacuum taken from the location they recommended. This post, although for a Series 2 actually has the information and photos which show where that is.

viewtopic.php?f=5&t=17366&p=142231&hili ... ce#p142231

I had a lot of issues trying to make it all work nicely, not helped by COVID which prevented me getting out to test things.

The car was fouling plugs quite quickly after the conversion and I nearly gave up but eventually sat down to work it out. It took some experimenting with the timing, which is a little difficult to do on the V12 without a ramp and or assistance doe to the timing marks location. See some recent posts and responses for ideas that help there.

Anyway, after playing around I think I ended up with the timing at around 15 degrees advanced at idle. That seems right and performance is in my opinion greatly improved, particularly in mid range acceleration. However, there was a long gap between the last drive of the car with the original setup and the one where I eventually got it all working, so I guess I might just be kidding myself!

I’m no expert but I did complete the conversion and I am very happy. Search my posts for more of the guidance I sought, received and applied. I just searched myself using my username and the term “advance”, which found most if not all relevant posts. Hope this helps if you decide to try it for yourself.