Engine Tuning issues Early UK Series 3

[vee12eman]

Hi,
Long time since I’ve posted on here, largely because my car wasn’t running well and I got frustrated and concentrated on other projects.

The engine was rebuilt by an acknowledged expert. I haven’t done recent compression checks, but believe they are good – I will check when I have more time. Carburettors were rebuilt, albeit by me, and I think are also good. As far as I can tell there are no induction leaks, but I am aware the V12 is prone to this and may require checking. Ignition system is a ReOpus unit, believed to be good. The car is very early UK spec with no emission gear. However, I feel the car is as not smooth as expected and it seems to run out of power rather early under acceleration.

A huge consensus recommend a Vacuum advance unit should replace the original Retard unit, with much debate whether the vacuum take-off should be Manifold or Ported (immediately after the throttle). I decided to pursue this avenue and fitted a Vacuum advance unit from British Vacuum Unit in the US, (unit number 54405202) and created a ported take off above the throttle shaft, just past the throttle disc, as recommended. This was around 4 years ago, but with other projects, Covid and the dreaded lockdown, the car saw little use. When I returned to the car post Covid, the car quickly developed backfire under even relatively mild acceleration. I initially changed plugs and with the new clean plugs and after tuning the backfire was gone. Various other issues meant the car saw little use until late last year, but the backfire returned.

On Saturday, I took another look, starting by inspecting and cleaning plugs, prior to balancing and mixture setting. Airflow at idle is now matched (it wasn’t bad) and two carbs seemed very rich (black and sooty. These were adjusted; all carbs had some reduction in mixture strength. To confirm I used a Colortune (a plug with a window allowing you to see flame colour). All are now Bunsen blue as recommended.
On a long run, the car was much better – no backfiring but still a little down on power as you rev – it seems to run out of power quite sharply as I accelerate and the drop is pretty noticeable. Idle was tricky, dipping low and occasionally stopping as I braked to a halt.

The car is timed as recommended by Jaguar as if it were still running retard. However, I suspect this should change. I am not confident how to achieve this in the best manner, can anyone advise me? I believe you raise the idle with the screws, to around 1500-2000, then adjust the timing until the fastest idle is achieved; until revs start just to drop as you advance. Now back off to the best idle, then lock the distributor and set idle speed correctly. Next head out and test the car, looking in particular for pinking/detonation, minor adjustments may be required. Is this correct or are there better ways?

I am not really interested in the debate between ported vs manifold vacuum, lots of research led to the decision to go with ported vacuum and I don’t want to enter that rabbit hole.

Frustration led me to talk to a local Jaguar specialist (I'm in Australia so fairly few specialists are available) who reportedly knows the V12 well, with an eye to getting him to tune the vehicle. However, he will not countenance the idea of a Vacuum advance and wants to return the car to original with a Retard unit before proceeding. I’m almost ready to accept this, after all it is as Jaguar intended, whatever we think. I am no boy racer, I just want a responsive reliable car and would like to enjoy the power without it dropping away sharply as I accelerate. Can anyone offer guidance to tune the car, retain the advance if it is an improvement, or return to retard if it is best for the engine, tuning accordingly and allow me to enjoy the car fully?

Please help if you can.

[bitsobrits]

Usually when a car "lays down" at higher revs/load it's due to insufficient fuel and/or lack of timing advance. Too much advance is usually apparent by loud pinking.

What is your actual timing setting at present? Was the distributor advance curve modified when you fitted the advance?

[MarekH]

There is nothing wrong with advance per se, just how much advance. With retard fitted, it only gives retard at very low rpm, so providing you have blanked off the bottom left hand carburettor vacuum port correctly, your only new factor is additional advance at mild throttle openings.

Since you haven't checked your timing, I would experiment with more or less static advance. Failing that, get a timing light and plot your curve.

You can always disconnect your advance and plug it and this should return you to the same position as the retard unit would have given at anything over idle rpm.

kind regards
Marek

[Woolfi]

Why do you ask an idiot like a car-machanic about advance or retard ?
Read a book like "Otto-Motor Management" from BOSCH ! Written from a lot of high qualified car engineers.
In this book is a written, that before programmable ignitions, nearly every motor between 1960 und 1980 had an ADVANCE capsule. Like Marek wrote it added roundabout 12 - 16 degree (crank) at light throttle to the static and centrifugal advance. With this additional advance the gas consumption is lower.
The EV12 had the retard capsule because of emission reasons at idle. The burning-temperature is higher and therefore the motors heats quicker.
If you want to add a advance capsule to your motor, you MUST connect the hose to the correct point in the carb. There is ONLY one correct point. This is a hole roundabout 2 - 4 mm in front of the 'round plate'.
- At idle there is nearly ZERO vacuum at this hole.
- At light throttle the border of the 'round plate' is passing the hole and the vacuum is high. The high vacuum leads to a high advance. This is good for a perfect combustion at light throttle and low gas consumption.
- At full throttle there is a low vacuum at the hole. Now additional advance for the ignition.
The discussion about the correct port for ignition advance is only between fools and people who know how this correct.
If somebody has to less technical understanding, he has enough brain to read a good book about this and understand.
From where do I know this ? I was driving a 5,3 in my EV12 and now I am driving a 6,0L with carbs and the motor is running PERFECT with the advance capsule and the CORRECT hole, which I have drilled by myself in the carb. Some Stromberg carbs have this drilling , but closed at the top if mountede in a EV12.
I you connect the hose to a point behind this 'round plate', you will have 30 degree of advance at idle, because at idle the vacuum is max in the manifold. I bought a car, in which a fool has connected the hose from the advance-capsule to the manifold. The previous owner just changed the retards capsule to an advance capsule. As a beginner I was searching THREE full years , why I had a very bad idle with a lot of missfiring. The owner before me had mounted a advance capsule and connect the hose after the carb. If somebody don't believe this, he shall measure the vacuum at this point at idle.
In the book from BOSCH there is a draw , on which you can see very clearly, where the advance hose must end in the carb. I am not able to put this picture into the forum.
I have learned in the last 23 years of ownership, that for advanced / more difficult technical questions I never, never ask a car mechanic. They told me a lot of junk. I was forced to read good books about carbs or ignition or ask car engineers, which have studied on a university. I needed secure knowledge and not rumors, blah-blah or believings.
Regards Wolfgang Gatza

[Woolfi]

I think the missfiring can (?) caused by lean mixture. The detect this, you need a wideband lambda measuring system in the car. You have to measure the mixture at driving, NOT at iddle.
IF (?) the air filter, the motor and the exhaust system is original and the original carb-needles are mounted, you can adjust the mixture at idle and because of the shape of the four carb-needles, the mixture is also correct at light, part and full throttle. The shape of the needle adjusts the mixture.
If you adjust the needles higher or lower in the carbs with the 6hex-tool, the change of the mixture is biggest at idle. The higher the throttle is, the lower is the cange of mixture if you change it by lets say 1 mm in the carb. You must understand the math (!) of the relation from needle to jet. At iddle the cleft between needle and jet is VERY small. Small changes of diameter of the needle at the end of the jet, cuse BIG changes in mixture. At full throttle the cleft is big. The change of the cleft area by changing the high of the neddle is MUCH smaller than at idle. This you must understand, that you can understand why you cant cure a lean mixture at high or full throttle with the cange of the position of the needle.
Without such a wideband lambda system in the car it is allways a little walking and searching in fog.
Regards Wolfgang Gatza

[bitsobrits]

After reading Wolfgangs comments, then re-reading your original post, it seems to me your description of ported vacuum as immediately "after" the throttle, may in fact be manifold vacuum. Can you clarify on which side of the throttle plate your port is located (engine side or atmosphere)?

[jagwit]

Ignition system is a ReOpus unit, believed to be good.

You can not assume the ReOpus to be good. My own 2+2 was fitted with ReOpus when the car still belonged to my friend. The car had a persistent misfire. Which could not be cured with timing setting, carbs setting and clean plugs.

He has a electronic background (like I do) and did an extensive investigation using my Picoscope oscilloscope. Long story short:
1. Reopus works on the exact same method as OPUS, only with more modern circuit design and electronic components;
2. ReOpus and Opus works like points where the dwell time is dependant on RPM;
3. Opus and ReOpus both produce increasingly weaker sparks as the revs rise. If you should have a coil with too high primary resistance, this could also contribute significantly to weaker spark (drop in power) at higher rpms.
4. ReOpus' (and Opus') success depends heavily on the integrity of the trigger wheel. We found two issues with the trigger wheel which no amount of sensor adjustment could fix:
a. Some of the ferrite rods in the trigger wheel were broken which led to no or weaker sparks or inconsistent sparks (less coil charge time) and
b. some ferrite rods where set too close to the centre of the trigger wheel (too far away from the edge and sensor) which again led to weaker sparks. Under full throttle, these weaker sparks could lead to no spark.
5. He decided to replace the ReOpus with Lumenition which the car still has today and it now runs strong till way above 5000rpm;
6. My recommendation is to fit Pertronics (using part no 9LU-1122A Ignitor II - as for OPUS dissy). This is AFAIK the best value for money solution in conjuction with a coil with primary resistance of not more than 1 Ohm.

[vee12eman]

Hi and thanks for all the replies and detail,

Firstly, a confession, I knew I should really check compressions and timing before starting, but I did time the car carefully around 7 months ago and it has hardly run since then, so I decided to trust it because I had limited time and wanted the car running for the next day, so I decided to trust the original timing. Anyone familiar with the V12 will know it is a little awkward to get at the timing marks, limited time prevented my doing so on Saturday but I realise I need to check this.

The advance curve was not modified but the distributor was in fact an XJS unit with 18 marked on the centrifugal mechanism weights, I believe this indicates an 18 degree mechanical advance. The distributor was originally fitted with an advance unit but although it came with the car it had never been fitted, the original distributor provided was fitted with a retard unit but had been so corroded it was damaged on removal from the engine. I ordered and fitted a retard unit when building up the engine years ago. The distributor centrifugal mechanism is well lubricated and moving freely. I recently replaced the ferrite rod rotor in case there was any damage to any of the individual rods, this was after the problems began and made no difference.

I have little experience or skill with engine tuning, I know much of the theory but seem to fail at application, I have read many books, but they don’t really seem to sink in. I’m no fool and built almost every single aspect of the car, body, suspension, paint and total assembly. The engine was professionally rebuilt, I did everything else, even paint. Sadly, my skills lean toward bodywork/mechanical rather than tuning/fault diagnosis, but I keep trying.

Woolfi, Marek,

I have followed your posts over the years and am deeply impressed, but I can’t always follow the detail of the tuning, I wish I could. I agree that most “mechanics” are no better than the books I could read. However, the mechanic I approached is considered no idiot and has long experience with the Jag V12 in all iterations, from the E-type up to and including the Bathurst winning TWR XJS variants and the XJR-15. I was rather surprised he would not consider the advance modification, but with his reputation I felt he would know more than I and after all, I really just want a reliable, tractable car.

Regarding the connection, I believe I misled in my original post. After much research, the tapping was drilled exactly where Woolfi describes, not as I implied, just past the throttle disc (round plate), but in fact, just before it, i.e. the air passes it before meeting the disc upper edge. The photo below shows the location.

This photo shows my carb - rear left with the take off. Not as clear as I would like:


This is from the Jag-Lovers sire and shows the location better. Mine matches this image (allowing for the fact the carb is from a different location):


There was no misfiring, rather the car suffered from Backfiring, indicating unburnt fuel in the exhaust – a rich mixture. This was borne out by the sooty plugs and indication of rich mixture with the Colortune and also the fact that weakening the mixture meant the car ran much better afterward, with no backfiring. However, Idle was liable to dip and the engine sometimes shut down on overrun.. There also seems to be less power at higher revs than I expect. However, I intend to cancel the mechanic and experiment a little more. I have no idea how to fit a wideband lambda system and I think it probably beyond what I am prepared to attempt, but I can keep on with the Colortune and also experiment with the timing.

Philip,

Thank you for your thoughts on the ReOpus, I agree assumptions can’t be relied upon, but; one thing at a time and there was definite evidence the original problem was mixture related. I will continue to pursue that and am fairly confident the trigger wheel is fine, as a replacement new item made no difference whatsoever. Does the Pertronix 9LU-1122A Ignitor II work with the Reopus Amplifier or is it removed and the module does all the work? I assume it would, but once again, I perhaps should not assume! Maybe then I will feel brave enough to carry out the modifications proposed.

Thanks All, I will have another look hopefully this weekend and try some of the suggestions.

[jagwit]

Does the Pertronix 9LU-1122A Ignitor II work with the Reopus Amplifier or is it removed and the module does all the work?

The Petronix is an all-in-one unit with pickup and ignition amp elegantly all inside the dissy. Only wires needed is Ground, 12V and Coil-. Only other item needed is the coil. Opus amp can therefore be deleted.

[vee12eman]

Thank you Phillip.

[lowact]

Whereabouts in Australia?

[vee12eman]

Melbourne.

[lowact]

Just down the road …
As per Marek and Phil, yr issues are not due to the type of the distributor but may be due to the distributor’s condition. May be due to a whole lot of other things as well and more than just one... To eliminate the distributor as a possible cause, I could lend you one (XJS, vac. adv. + matching coils), to see if it makes any difference? (Could do the same with carbs .)
With the engine rotated to exactly TDC, is the rotor pointing at the left headlight?
My understanding, yr current distributor is a vacuum retarded type from an early xjs that had been “reopused”; to this you have retrofitted a vacuum advance module? Can’t be done like that. For now, disconnect and plug the vacuum offtake to the distributor …
My understanding, yr timing if “recommended by Jaguar as if it were retarded” would be 4 deg after TDC at idle? If so, because you don’t have a retard module, such a setting would be crippling yr performance. Instead, with the vacuum disconnected and plugged as above, use a timing light to set the timing to 12 degrees before TDC at idle and check that at 3000 rpm this increases to about 36 degrees before TDC. Then go for a drive and enjoy.
If there still are issues i’d suggest yr 1st next step should be to check yr manifold vacuum. Also consider installing a new fuel filter element, the crud is captured inside, you can’t see it, a midnight trip from melb to Canberra once took 13 hrs due to blocked fuel filter. Also check yr fuel pump pressure; because rich at idle doesn’t mean you are not being starved when trying to accelerate …

[madjack4]

Hi reading all the posts no one has mentioned to check the main diaphragms in the carbs . These days all the rubber parts u buy are poor quality i would remove air filters and rev it up while watching to make sure that the slides are all lifting and topping out on full throttle

[jagwit]

i would remove air filters and rev it up while watching to make sure that the slides are all lifting and topping out on full throttle

I don't think one should expect full lift of those air valves without the engine being under significant load and at high revs. Never tried it myself though, so I don't know this for a fact, just gut feel.

[vee12eman]

Hi and once again thank you all for some great input. I have a long weekend coming up so will try to find time to do the following:

Confirm timing – Static and dynamic
Inspect the distributor weights mechanism – believed to be free, but no harm in checking.
Check the lift of each carb piston, believed good, but as above. (Thank you madjack4)
Check fuel filter, actually changed quite recently, but as above.
Set timing to 12 degrees BTDC, check for advance to around 36 degrees BTDC at 3000rpm, then road test.

Additionally, I will be using new Champion N9YC plugs and fresh 98 octane petrol – the current tankful still contains some oldish fuel, mixed with new fuel from the weekend.
If anyone has further ideas, I’m open to hearing them.

Colin,

Thank you for an amazing offer, I have had real difficulty finding anyone in Australia, let alone Melbourne who I can compare notes with, let alone borrow parts for fault diagnosis. Whereabouts are you, or would you prefer me to PM you? Please feel free to PM me any contact/location details if you don’t want to post them here. Also thank you for reading my posts accurately, I see that I may have come across as a little foolish, or at least naïve. Hopefully I am not the former but happy to accept the latter!

I entered the recent round of tuning to get the car running for a 200km round trip on Sunday. The car performed quite well, but I think could be better. Time prevented full checks including timing etc. – if the car had not run reasonably well on the test run late on Saturday, I wouldn’t have gone. The improvement, with backfiring in particular no longer present, was dramatic and I felt it worthy of going. I wanted a longish run prior to getting more serious with diagnosis. My statement regarding timing being “stock” was my best recollection of the last time I tuned the car, but I’m pretty certain it was a foolish statement and that the ignition at idle was somewhat advanced, it certainly isn’t 4 degrees after TDC. I would have known that was a bad starting point but of course should have established the actual setting. In answer to another point, yes, with the engine at TDC, Firing stroke, the rotor points at the left headlight.

The experience has led me to check the history of the car, confirming just what is fitted. Without going into too much depth, here are some findings, from checking my records and photos.

The car was dismantled, in terrible condition when bought, but original and unmodified. It is an early car – the 97th RHD 2+2 FHC, UK spec with automatic gearbox.

I rebuilt the car completely, converted to 5-speed manual, during the process I migrated from UK to Melbourne. The first time I started the engine was in Australia.

The engine was sent for rebuild prior to leaving, as I had none special tools and time was pressing due to the move Down Under. I needed the car basically complete, for import purposes. The guy who rebuilt the engine, Brian Ball has a great reputation although he operates largely on word-of-mouth recommendation, so is not as well-known as some. Due to issues with the terrible condition of the original block, it was rebuilt using an XJS non HE block and heads, serial 8S11***SA, with as many usable parts transferred from the original engine as possible.

The distributor body was damaged beyond repair when removed (not by me) from the engine. A second hand replacement was obtained and I believe it is from a Pre HE XJS. Photos of that unit show it fitted with a Vacuum Advance unit on arrival (vacuum intake points away from the distributor body). From memory, that vac unit had a punctured diaphragm. It has 18 degree weights fitted.

In one of my early demonstrations of naivety, I simply replaced the advance unit with a retard unit, as this was original to the car. I was aware of the supposed limitations of a retard system, but not confident enough to try the conversion at that time. I bought a ReOpus Unit from Dave Curry of ReOpus and followed his instructions to ensure the unit he supplied worked with the setup I had, he was aware of the distributor, amplifier and car model and the discrepancies between them. Biggest issue was the supply to the tachometer, but with his assistance, this was overcome.

Carbs were totally rebuilt, including new correct spec needles (I think they are different on manual vs Auto, from memory, possibly not) New jets etc. were included in the kit. I had two sets of carbs, so was able to replace some parts with better as required.

Plugs are NGK BP5ES, not particularly old. Rotor Arm is a New Old Stock Lucas item, cap is from SNG, again not particularly old. Pump is original with a rebuild kit and operates well. The fuel return circuit operates with the proper “fizzing” sound evident from the Pressure relief NRV.

The Vacuum advance unit is a 54405202 unit and has the ability to adjust the level of response to the vacuum. It was recommended and supplied by British Vacuum Unit, who responded to my enquiry, advised me on the best unit (of the many they supply) and advised on the location of the port to drill for the ported vacuum take-off – this matches the location of several other Stomberg ported vacuum take-off points, notably the triumph TR6. The hole is .54” before the exit into the inlet manifold, placing it just before and above the throttle disc of the left rear carb (relative to inlet airflow). See pictures in earlier post.

I can’t think of any further relevant points but Colin, I would love to come up and look at your projects, share notes and possibly take you up on the offer of a loan, hopefully, you don’t regret the offer – I will understand if you do.

Thanks to you all once again.

[lowact]

There’s specialists around but it’s like yr Brian Ball, they don’t advertise it’s all word of mouth. I’m just a retired engineer, learning from my mistakes. Barton in Canberra, happy to meet and loan, I’ve added you to the list of people to show off to if I ever finish modding my car …
Pre HE distributors were all retarding type. So if it came with a vacuum advance unit it shouldn’t have, reverting to a vacuum retard unit was the correct thing to do. Now you’ve fitted a vacuum advance unit (54405202) so it seems yr distributor and vacuum unit may be incompatible? Consequence would be that the vacuum module just wouldn’t do anything, Like many people you would have mechanical (centrifugal) advance only. To test this, suck on the hose that connects to the vacuum module, if advance is enabled your sucking should rotate the distributor (pick-up sensor) clockwise some 20 degrees?
Your left rear carb has a tapping point underneath, hard to get to, is where the vacuum MUST be taken from for a vacuum retarding system, this ensures that retarding only happens at idle. You’re not using this, has it been properly blanked off?

[vee12eman]

Colin, thanks again for the input and offers. I will be very interested in your mods, the GasCat looks seriously cool, how do you feel about making double quantity of everything…!? Just joking of course, but I wish I had the knowledge/skill/confidence to undertake such a project.

Whilst I am fairly positive your knowledge is vastly superior to mine, there is one question that I have regarding fitment of Pre-HE cars. Evidence I have found suggests that at least some pre-HE cars were fitted with Advance units, but it seems Australian cars were late to the party. Perhaps this is where the confusion enters the scene?
Anyway, the data comes from the Jag-Lovers Site, where Mike Morrin did some research as long ago as 1998. The link is here:

https://www.jag-lovers.org/lists/archiv ... 00081.html

In a more recent post he has recognised that unit 41677 does exist (See the link for more detail).
I had no way of adding the data to this post, except to create a table and screenshot it, but below is my best effort at that for quick reference. Note the original post and some of Mike's follow ups give more complete information. Note that 41622, 41640 and 41642 are all indicated as Advance units fitted. I therefore believe there is a possibility my distributor, which came with an advance unit fitted and is believed to be pre-HE, may actually be as original and correct. I'm still searching for more detail and will also try to find the part number on my distributor at the weekend.



On another note, the tapping for retard, under the carb, has been blanked off. I’ll test to see if the unit does in fact advance timing with suction as soon as I am able.

[vee12eman]

So a bit of follow up. I did some research and discovered there are definitely other Pre HE V12 cars that were originally fitted with advance units. The XJ12 Series 2 cars were fitted with distributor 41742A, which is the one that I bought for my car way back in around 2006 or 2007, before I knew anything about the system, other than that my original distributor was beyond saving. It arrived correctly fitted with a vacuum advance unit, at least, correct for XJ12 cars not for the Australian and, I believe the Canadian markets. This was not listed in the data I originally found and I am still trying to confirm that absolutely, but various sellers list an advance unit for the XJ12 S2 in the rest of the world, with retard in Australia.
Accordingly, I have stayed with the advance unit, meaning that I had to find another answer to the issues.
I was much busier than hoped last weekend, so had to choose between options.
I believed timing was the root cause, so I had to placed the car on blocks allowing me to fully open the bonnet, fit an extended, fixed bonnet stay to hold it fully open and place a mirror, allowing my timing light to illuminate the timing marks on the lower quadrant of the pulley wheel, between the coolant hoses, alternator and other components on the front of the engine. It’s fun timing an E-Type V12,especially if you have no-one to help!
Anyway, timing, with the vacuum unit blocked off, the timing was around 9 degrees, advancing it to 15 degrees greatly improved the idle, so was the figure settled upon, then idle was balanced at 800 rpm and the car lowered, the bonnet stay refitted and the car tested.
The performance is transformed, and I have yet to check the mixture, although I believe it to be fairly accurate at the moment. The car even ran slightly cooler, a benefit on a warm Summer day.
Still some work to do, but definitely on the right track.

Thanks again for the pointers and guidance.

[lowact]

Next time consider using an endoscope that plugs in to your phone (camera). Attach the camera end to a block of wood that you can move around on the floor until the timing marks are in focus. The timing light similarly mounted. Place yr phone (display) next to the distributor ...