V12 Running issues

[andrewh]

Hi Guys, this question actually relates to my XJ12 series 1 1973 but should be much the same for a similar age E.

Basically, she is running really well when I boot it, definitely on 12 but seems to be fluffy at constant revs. I cleaned all the plugs and one or two were oily. Actually on the left bank the very front and the very rear as well as one on the other bank. I only did about 20 miles and the problem is back. Any ideas? Could it be mixture or something else?
Also, takes for ever to warm up and needs loads of choke which I hate giving it. I wonder whether that contributes to fouling the plugs. Anyway its one of those issue, that could be iginition or could be carburation or could be something else. Any ideas? Oh and I only get 11mpg, what does a V12 E do? thx

[Phil]

hello Andrew,

I am not a technical expert, but would probably suspect carburation issue? But I hope our technical knowledgeable forum users will get back to you with more/better insights.

Oh and I only get 11mpg, what does a V12 E do?

My last 3600 miles driving (mixed driving) recording gives :
19l/100km, 12,4 mpg US, 14,9 mpg imperial

my best average was when driving from Belgium to Goodwood (670 miles, mainly highway at 70 mph avg) with 15 l/100km, 15,7 mpg US, 18,8 mpg Imperial.

hope you find a solution soon

[andrewh]

Hi Phil, thanks for the reply. I am pretty convinced its carbs now. I tried to balance them yesterday but discovered that two are drawing more than the other two. This may be internal to the engine, but I doubt it. I am thinking its all to do with the temperature compensator and other other carb issues. Will keep you posted

[WDRV12]

Usually we find just about every V12 we get in with running problems are usually down to very silly things, and here are just a few I have had in the last couple of weeks
1) Ignition timing. How many dealers and independants have I seen that dont know how to use a timing light ... Its just amazing that if they cant plug in a computer then they just walk away. It is a 2 man job to get it right as one needs to check that the centrifugal advance works whilst the other sits in the car and runs the engine to the desired rpm (9 out of 10 distributors have siezed and it will cost you at the pump if it is ).And trying to see the scale on the front damper can be a bit awkward as the oil filter can get in the way. At least 1/2 the cars we see have faulty vacuum advance /retard units leaking ( Just start the angine put a piece of pipe on it and suck and you will notice immediatly if the engine note changes. If theres no change then here's a good one for high mpg and poor and eratic idle , a V12 you should be able to balance a coin on at 3000 rpm !
2) Silly one but loads forget : Carb dash pots empty ( applies to both Stromberg and SU converted cars) or half full of oil ! use a fine 3in1 or even ATF oil will do fine , if the dampers in the carbs cannot work correctly then the engine will tend to gulp air and usually feel like its holding back. It must be checked every 2 weeks not every 2 years because you have only done 300 miles !
3) Perforated diaphrams (strombergs only for this one ) often found when the car is laid up for long periods or has had the gentle hands of a mechanic shaped like a gorilla ! The other one on this is the diaphrams incorrectly located !
4) A bank running richer than B bank , If all the needles are at the same hieght then you can bet your shirt that there is either insuffecient fuel supply from the fuel pump (pressure and volume) or that the filter that you friendly dealer charged you for the other day is still fresh from 1975! The filter is located in the boot on 12's and is a throw away element and its hidden behind the spare wheel in the right hand corner. If your changing it then do it out side and get lots of rags ready as you will spill a bit of fuel. Be very carefull not to go mad on the glass bowl equiped cars as these dont bounce when you drop them !
5) Throttle linkage ... I have to do this one nearly every couple of days on the cars here . In the last week we have had six v12 E's in and 5 of them needed the throttles resetting. It takes time to set up 4 carbs but its really worthwile when you have got it right. Its even more fun when you have six webers
6) And the best one yet is the nice chap that fitted his own plugs before bringing it in and thought the HE plugs would be easier to fit than the originals ! They have the wrong heat range and have totally different seating washer !

Dont try to set up the carbs untill the spark is right as your just throwing away good time and money..... BP and Shell would like it though :D

[MarkE]

That's great advice, Richard.

As a bloke who's seen all the variations on the V12 in an E Type, which way would you go as the base for a car that's used just as a fun classic, but makes the most out of having a great big V12 in the front?

Original Strombergs
SUs
Webers
Injection.

Now that my S1 Coupe is finished, I'm starting to think seriously about what to do with my S3. I've got a few options here accumulated over the years..

Firstly, I've never had problems with the Strombergs that are fitted, but obviously have read over the years that they restrict the engine in favour of emissions.

I have a set of the correct SUs, linkage and manifolds, but I'm really unsure whether or not they would give much advantage.

I've seen, and more importantly heard, a couple of S3s with webers, and whilst they seem the most exciting option, I really don't want to end up with a car that does 5mpg...I want to enjoy it a bit more than that! Is the 5mpg just pub talk?

I have a few XJR-s 6 litre cars, and one of those has a stunning engine, but rather ratty bodywork...so you can see where my thinking is going with this one! I guess that the supplementary on this option is...keep or junk the Zytec if used in the S3?

I'm looking to build a car that's fun and thoroughly usable and reliable on the road, probably with a little more performance and a lot more V12 soundtrack!! I guess that unless the weber option is pursued, then most of the soundtrack will come from the exhaust side rather than the induction.

Any thoughts would be appreciated.

Mark

[andrewh]

thanks for the really comprehensive run down. To be fair I have checked a lot of that but its probably worth checking again as it was some time ago. The thing that really gets me is that my distributor has a vacuum capsule on the side of it, but does not have the vacuum pipe attached. The carb outlet for this appears to be plugged with a rubber bung. So no advance or retard which ever it is by vaccum. Is this correct in your view? I think the distributor was a swop for a SNG Barratt opus replacement system before I bough the car.

But the really strange thing is the much greater draw on two carbs vs the other two, when all the throttle linkages have been adjusted.

[WDRV12]

thanks for the really comprehensive run down. To be fair I have checked a lot of that but its probably worth checking again as it was some time ago. The thing that really gets me is that my distributor has a vacuum capsule on the side of it, but does not have the vacuum pipe attached. The carb outlet for this appears to be plugged with a rubber bung. So no advance or retard which ever it is by vaccum. Is this correct in your view? I think the distributor was a swop for a SNG Barratt opus replacement system before I bough the car.

But the really strange thing is the much greater draw on two carbs vs the other two, when all the throttle linkages have been adjusted.

Ok only 3 for this one
Either air leak on manifolds or
tappet clearance very tight or
you may find cam timing out on 1 bank , and this one we see a lot of recently for some strage reason :?

[WDRV12]

That's great advice, Richard.

As a bloke who's seen all the variations on the V12 in an E Type, which way would you go as the base for a car that's used just as a fun classic, but makes the most out of having a great big V12 in the front?

Original Strombergs
SUs
Webers
Injection.

Now that my S1 Coupe is finished, I'm starting to think seriously about what to do with my S3. I've got a few options here accumulated over the years..

Firstly, I've never had problems with the Strombergs that are fitted, but obviously have read over the years that they restrict the engine in favour of emissions.

I have a set of the correct SUs, linkage and manifolds, but I'm really unsure whether or not they would give much advantage.

I've seen, and more importantly heard, a couple of S3s with webers, and whilst they seem the most exciting option, I really don't want to end up with a car that does 5mpg...I want to enjoy it a bit more than that! Is the 5mpg just pub talk?

I have a few XJR-s 6 litre cars, and one of those has a stunning engine, but rather ratty bodywork...so you can see where my thinking is going with this one! I guess that the supplementary on this option is...keep or junk the Zytec if used in the S3?

I'm looking to build a car that's fun and thoroughly usable and reliable on the road, probably with a little more performance and a lot more V12 soundtrack!! I guess that unless the weber option is pursued, then most of the soundtrack will come from the exhaust side rather than the induction.

Any thoughts would be appreciated.

Mark

My choices are 1)
Strombergs are very good but hardly any one seems to get them right but they have suffer from poor maintenance and are developed for thier emmissins advantage more than power. It should be remembered that the Group 44 Tullius V12 did run strombergs and could deliver near on 450 BHP !

2) SU conversions .....hmmmm I have to bite my tongue a bit here. Do they really give more power and MPG over the Strombergs if they were corrctly set up ??? errr not a lot but they are easier to tune as a whole load more people understand them !

3) Webers OK I am biased on this one, 5MPG no at least not when i drive one !! I have a 7.7 with 6x 44mm and she returns over 18, every V12 i have built for my own cars are either on webers or multi throttle injection. Instant throttle response ..... The soundtrack is as good as Andrea Bocelli on a perfect stereo ..BUT the kit from SC is cheap compared to others but it needs a lot of fettling to get right ! Throttle linkage is not very good, port matching needs to be done, and they come without trumpets or air filters !

4) Injection Off the standard v12 works very well but its not a five minute job , but will give you good response and better overall economy.
5) Throttle bodies is the perfection, big power with instant throttle response but don't think these come easily on the wallet. You will not get any change from ?7000 by the time its fully mapped and ECU's are not cheap. But you can get very very good MPG and power.

[MarkE]

A great summary, Richard...thank you. I think that the SU set is destined for eBay now!
Mark