S3 V12 Stromberg/Dizzy vacuum pipes

[muz122]

Hi all,
My first post here and I would be extremely grateful to receive some of the wealth of knowledge evident in this forum.
I'm a JLR tech here in Thailand and have recently taken on a restored 73 S3 in need of setting up. I've plenty of experience with classics but the issue here is not knowing exactly what is original/modified/bodged from previous workshops.
So, the car was delivered to me running a bit lumpy, popping on overrun and definitely rich smelling. I decided the first thing to address were the carbs, so ordered a complete Zenith rebuild kit and a set of Magnecor plug leads.
Found several problems when rebuilding the carbs; dissolved bypass valve diaphragms, incorrect float heights, perished needle adjuster o-rings etc.
All rebuilt and refitted, carbs synced and mixtures set to 1 turn out from fully seated.
Engine starts easily from cold and hot, idles but spits flames from the carbs when revving. It didn't do this before but the timing and other settings may have been adjusted to compensate for tired carbs etc.
So I obviously need to check the ignition timing (any links to the procedure would be much appreciated) but before doing that, I need to make sure all vacuum pipes are in order.
Starting at right bank (drivers side). There is a single pipe joining both carb bypass valves together. Another pipe joins choke on front carb to a port above temp compensater on the other carb.
On the distributor, the vac advance (or retard?) unit is on the rear of the distributor body. There is a vacuum pipe from the advance unit with is connected by t-piece to the pipe that connects both carb bypass valves together on the left hand bank. It doesn't move when sucking the pipe.
Another pipe joins choke on one carb to a port above temp compensater on the other carb.
The rear left carb has a blocked off pipe underneath, rear of the float bowl.
Front right and rear left intake manifolds have a plugged opening.
Ignition amplifier is Lucas OPUS.
I renewed the plug leads one at a time so they are definitely not incorrect (unless they were wrong in the first place!).
It's already a lengthy post so I won't complicate it further, but if anyone things something is amiss from the above setup, or has any ideas, I would be super grateful.
Thanks in advance

[vee12eman]

Hi Muz122,

A couple of things from your post. The vacuum unit appears to be the original retard unit, with take off pipe facing the distributor. Loads of opinions on what you should do about that; many favouring conversion to advance unit and then loads more opinions about where to take the vacuum source. Others use no vacuum unit at all, just blanking it off. I am not getting in to that, plenty of info on the forum if you search and I have not sorted through that with sufficient confidence to deviate from standard.

In standard form, the take off for the retard unit vacuum is from the tapping under the left rear carb, which you said was blanked off. As stated earlier, many blank that tapping anyway, doing without a vacuum unit at all and, as you say, your vacuum unit does not seem to move when sucking on the pipe. No surprise there as they were famous for failing. If it really has failed, then the connection it makes now is providing a vacuum leak (through the failed diaphragm) and one of the things I can say with certainty is that this engine set up does not like vacuum and inlet tract leaks.

The distributor internal photo shows that it is not, in fact the original Lucas Opus set up. That has a very different rotor and pick up, I will try to find a photo. It does appear to be an inductive pick up, so may be connected to a Lucas Opus unit, but who knows if they are compatible? It may be a different electronic system installed inside the original box. I guess the yellow mark indicates the lug for plug 1A, if you turn the engine to the firing point for no.1A cylinder (10 degrees before TDC if I recall correctly) and align the distributor so that lug is aligned with the pick up sensor, then you will be in the ball park for static timing, provided the lug really does align to 1A. You will need to dynamically time with a strobe gun and because the timing marks are on the lower edge of the front pulley, this can be difficult working alone.

As the car runs, you can probably assume the ignition components are compatible, but no guarantees there.

I suggest starting by identifying the correct vacuum set up for your car, this will differ by date of build, delivery market and (possibly), aftermarket modifications. Next, decide whether to us vacuum advance, retard (including the take off point - see other posts for this) or just blank off both the unit and take off point. Next ensure all air leaks are eliminated and blank any unused vacuum points. There are a lot of potential leak points and all can have significant effect. Set timing as best you can statically and use a timing strobe gun to get it right. Next you will have to balance the carbs with an air meter. It's like balancing three sets of carbs, first one side, then the next, then balance them across the car. Mixtures can be set with a Colortune (Google it) or by me using the piston lift method used on Stromberg or SU carbs (contrary to popular belief, that works well provided the lift of the piston is very small and consistent).

If you don’t understand the description above then you either need to learn or find someone who can do it. I can send an article on carb tuning and balance I wrote for the E type club some time back which may help if you pm your email address to me. It may help make the tuning easier.

Good luck,

Simon

[muz122]

Hi Simon,
I can't thank you enough for your informative response. I've ordered a new dizzy cap and rotor arm as they were showing some wear, so I'll tackle the timing after they arrive.
I'm still a bit puzzled over the pipes between carb bypass valves. I'm assuming they should be vacuum actuated. In current set-up, the RH carbs are linked together only, with no vacuum supply, so not actually doing anything? The LH bank carbs are linked together and with the dizzy vac unit, so also not doing anything! Maybe that was done by the previous workshop as they knew the bypass valve diaphragms were shot....who knows!?

Thanks again,
Matt

[Bob.]

Hello Matt,

You will find the original vacuum pipework layouts in the Parts Manual under section 30 - see the forum knowledge base (you need to be logged in to find this). As Simon says above the system will depend on build date and market the car was originally supplied to. Note that there is an additional vacuum pipe from the rear of the LH manifold to the gearbox if it is an auto.

You will find the USA Specification Driver's Handbook useful as it has 39 pages covering the emission control system (this information is not in the Workshop Manual). I haven't seen the handbook in the Knowledge base but reproductions are available for a reasonable sum. eg https://www.sngbarratt.com/uk/#!/Englis ... 55767067c6

In your first post you say "Another pipe joins choke on front carb to a port above temp compensater on the other carb". Only one carb on each bank has a choke valve but the output from it is shared with the adjacent carb via this pipe, so all four carbs actually receive additional fuel.

Hope this helps,
Bob

[muz122]

Hello again,
Not had much time to work on the E type lately due to other work commitments, but now have the new dizzy cap and rotor arm fitted, vacuum pipes (hopefully) sorted, timing set to 12° BTDC (as per manual).
The issue I've ran in to when balancing the carbs following the service manual procedure (all idle trim and balance screws slackened off, set idle to 650-750 using RR and FL carbs idle trim screws, then balance FR and RL using balance screws). All ok up until step 13 of procedure, 'screw in left balance screw until RL carb hiss matches FL.' Tightening the screw doesn't actually rotate the throttle spindle in the direction required to open the throttle, so I'm wondering if the linkages have been wrongly fitted, which brings me to my question/request, does anyone have a picture of the left bank balance screw setup please?
Also something that doesn't seem to be mentioned, when adjusting the balance screws obviously the idle is increasing above the initial 650 RPM base setting. Do you ignore this and match all the carbs perfectly, then reduce the idle speed by backing off the RR and FL carbs equally?
Thanks again,
Matt

[42south]

Hi
Looking at the picture of your distributor I’m fairly certain that it’s the HEI distributor as used in the later V12s.
It looks so new inside that I’m thinking that it may be the unit sold by SNG Barratt, if so it has the upgraded electronics packaged in the original Opus box which is visible in the picture, It is the retard vacuum unit, and you would be well advised to just leave it blanked off, it hurts performance and fuel economy, and was only ever there to try and meet USA emission standards, the car runs better without it.

All that vacuum piping between the bypass valves could be removed as well, and the valves just blanked off, as you are probably aware their sole purpose is to enriched the mixture slightly on a snap throttle closed overrun situation to prevent that popping in the carbs. Their adjustment is possible but quite a procedure. I run without them with no problems other than a nice pop pop pop on the overrun, sounds sports car like to me.
The temperature compensators beside them are another source of problems, and many people including me have just screwed down the adjusting nut till they are no longer functional.

A link to some discussion

http://forum.etypeuk.com/viewtopic.php?t=11048


Cheers

[42south]

Hi again
One other thought regarding distributors. Jaguar, after a couple of distributor cap explosions, due to vapours leaking into the cap, changed the cap to a vented one.
These are available thru the usuals, and have two ports on them, one is connected to the rear of the air filter canister to provide a small positive suction, and the other one goes to a small air filter to allow fresh air into the distributor. I used a small ride on mower filter for this purpose, and just tied it to one of the engine mount frames.
Cheers

[Geoff Green]

The distributor air inlet filter was a push on small fuel filter connected to the distributor with vacuum hose, no clamps used. The filter was loose in the v of the engine.

[muz122]

Thanks all for the advice, much appreciated. One thing I'd overlooked, timing of 12° BTDC is for 97 octane fuel. Here the fuel is 95, so should be 8° BTDC.
Something else i may have messed up on is the jet height. In the instructions which were included with the carb rebuild kit, it states 'the new jets should be pressed in so that the top of the jet is below the bridge by the same amount as the old jets'. This sounds like more of a depth/recess. I set them to flush as per someone else's recommendation, however, other posts are referring to a jet height of around 2.5mm above the bridge. Is there a standard setting? Please don't ask what the original jet height was

Thanks again,
Matt

[Bob.]

The outer land of the fixed jet face should be set 0.1" (2.5mm) below the level of the bridge. With the correct needles fitted there should then be enough adjustment available via needle height to tune correctly.
Bob.