Ignition timing Australian delivered car

(jeff) #1

I’m confused.
The car is a 1978 build XJ12, Australian delivered.
For timing, the Manual says for for US and Australian cars 1977-78 the timing is 4 After. Others 12 Before.
The car does not have an air pump which I believe US cars had.
The only change made (that I’m aware of) is an SNG Barrett Ignition upgrade - Distributor,Amp, Coil & Ballast Resistor.
Any help much appreciated.

(baxtor) #2

I am not sure how this might relate to your inquiry but the aussie cars (at least for a time) had a vacuum RETARD unit while on most others it advanced the timing.

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #3

In the Book, I spell out an improved timing scheme for the pre-H.E. that involves setting the timing at 2000 or 4000 instead of at idle in order for the timing to be more accurate where it counts, near the peak of the torque range.

(jeff) #4

Thanks all.
So assuming the original different specs were for different emission regulations and I have now changed distributor etc I should now go with the normal timing?
The original specs also said to time it with vacuum hose on.
Finally, Does the timing also depend on octane rating of fuel used?

( 1971 S3 etype : Ohope beach New Zealand) #5

Hi Jeff
Is your car one of the lower compression engines, this could make a difference.
The Sng kit supppied for the pre He engines, like mine, has a vacuum retard module fitted to the distributor, as per the original. Check and see if yours has this, if so, blanking it off will help fuel consumption and performance.
My car has a pre he high compression engine, with the sng kit, and runs happily at 12 deg btdc timing vacuum disconnected, and has no issues with the 95 octane petrol in NZ.

(jeff) #6

Thanks Mark
I don’t know if it’s lower compression so does engine number give indication?
Can’t see any module. Where is it located?
Just appears to have the vacuum hose.
Please excuse my lack of knowledge. I have tried to read up on all this but have got myself confused.
Anyway, going with the 12 BTDC.
I was using premium 98 octane.

( 1971 S3 etype : Ohope beach New Zealand) #7

Hi Jeff
The vacuum module is the silver thing on the side of the distributor.
It should have a vacuum hose connected to it, which should go to a vacuum source underneath the left rear carb.
If you have that config, disconnect both ends of the vacuum hose and plug the pipes, your car will go better.
I think the engine number will identify the compression ratio, post it here and someone should help out.
Maybe a search for low compression engine or similar will throw up the info you need.

(jeff) #8

Well it’s low compression- LA suffix.
Looks like I follow the manual. 4 deg after TDC. Have no idea why such a difference. US and Aus had stricter emission police?
It’s injected and the vacuum hose leads to the RHS throttle body.
Are there any other suggestions?

( 1971 S3 etype : Ohope beach New Zealand) #9

Hi Jeff,
Have you downloaded Kirby’s book on the V12, there is a link, and it’s free.
I have heard mention of a tan coloured owners manual that has a diagram of all the vacuum pipe work on your car, it would be well worth while getting a copy.
Remove all of the emissions control stuff that you can, the car will go better, and it removes many sources of vacuum leaks.

(jeff) #10

Thanks Mark

I Have Kirby’s book and have read up on this.

Think I’m getting there.