123 or standard Lucas dizzy on uprated engine

[andrewh]

I have now finished running in my 3.8 engine and started to open it up a bit on occasions. I am starting to wonder whether the advance curve in the standard distributor, ( rebuilt by Distributor Doctor) is correct. The low end performance and torque is exceptionally strong, quick and smooth, but above about 4000 rpm it seems to be less reluctant to rev. I have done quite a bit to the engine.

Bigger Inlet valves XJ6 series 3
Fully Gas flowed
Fully Balanced
Rob Beere Fast Road SU Cams
Sports air cleaner.

So all of this has led me to fit UO needles, which seem ok, although it could be that its getting a bit lean up the rev range. I will have to take it to a rolling road to work that out. Someone suggested to me that it could be that its running out of advance on the standard distributor.

I must confess that without this being argued to me, I am not sure whether that makes sense or not. I would have thought that required advance curves are not altered by the work I have done as above. My work is all about getting more fuel and air into the engine, and I am sure its a weakening of the mixture due to the increased air flow I have. It has been suggested to me that I should think about UVO or UVR needles as they are substantially richer in the higher throttle opening range than the UOs that I have fitted.

Of course I can try a set of either of those needles and see how it performs , but the suggestion of a 123 distributor with a different advance curve needs selling to me. I am all ears!!!

Over to you chaps.

[christopher storey]

I'm not, I'm afraid, an enthusiast for the 123 . When you get a good one, they are fine and the theory of them for bespoke tuning is a good one , and thus I can see the attraction for you in your particular circumstances. However, in the group of 20 or so cars with which I am very familiar, many of them Jaguars , we have had several sudden failures and had to throw them away . All I can say is that, as with any electronic system, I would never leave home without a spare , purely mechanical , distributor in the spares kit

[cactusman]

And there is another recent thread detailing the woes experienced with a 123 system although they seem finally to have been resolved. Trouble with the 123 is it has some sophisticated technology built into the distributor. Fine when it works but if it fails you are stuck and so will the RAC or AA etc. I would say that unless you need every last horse then stick to a more conventional system using a powerspark or similar module....mine seems fine after nearly five years and it would take 20 mins to pop the points back in....I carry them in the boot. Get the carbs correctly set up with the right needles on a rolling road...job done.

[Gfhug]

Andrew, your comments about needles could be correct, but difficult to tell without a proper test at all the revs and trying different needles. That can be a lengthy process. Might be best to get that done soon.

Geoff

[Heuer]

EDIS/Megajolt is the only game in town for optimum performance. Although Ray's kit is no longer available you can put one together using parts from http://www.Tiggerwheels.com

If Megajolt fails (unlikely) EDIS continues in limp home mode which will easily get you to your destination albeit with static timing.

[andrewh]

thanks chaps. I knew I would get the " dislike the 123" comments, but was trying to avoid that. I am more interested in what a 123 that works can achieve over a standard distributor. Presumably the 123 with its different advance curves has a dynamic over and above a standard Lucas?

[abowie]

The standard advance curve is biphasic in shape because of the 2 springs.
Maximum advance is dictated by the cam; once there is enough centrifugal force applied by the weights to bring it to the end of the cam it can't go any further. This is supposed to happen before 3000 rpm.
So your mechanical distributor will always be limited in how much advance it can give you and this should all be happening before you are having problems at 4000 rpm.
You can map your current advance curve by using an adjustable timing light. You can also measure maximum advance on the distributor using a protractor. If necessary, once you know what the curve actually is you can adjust the curve, and maximum advance, by modifying the springs and the cam.
The adjustable 123 makes this part easier.
I agree that you need to dyno the car to get an objective idea where you actually are. Personally I'd stick with the Lucas dizzy unless you come to a point where it is clear that it can't be made to do the job for you.
Cheers

[andrewh]

Thanks Andrew, thats vey helpful. I did actually advance the ignition 4 clicks on the Lucas distributor as an experiment and she did feel more lively. As you say, I think its off to the rolling road. I am also awaiting a call back from Rob Beere who may have some advice on both jetting and advance curves.

this is chart of the different profiles, hence richness of the various suggested needles As you can see the UO I have fitted is quite a bit leaner than the UVO and UVR. Ignore the yellow one its a spurious entrant.

[abowie]

This is a good read.

Distributor Tuning

[Hugo]

"Biphasic". There's a good Scrabble word! Anyway, you don't need a rolling road and a dozen needles to see if it's running weak at high speed - all you need to do at this stage is pull the choke on a click or two and see if it improves. If it does, then you know you are on the right track and can explore further. If it makes no difference, you can start looking for another cause.

[andrewh]

I have pulled that trick many times over the years to check mixture, but not sure it would work on this experiment as the effect of pulling the choke on is to choke the air not increase the fuel flow. So net net, not going to achieve anything I would have thought?

[Hugo]

Not on an SU it's not! It just drops the jet down a bit. It isn't a 'choke' at all, it's an enrichener.

[PeterCrespin]

I have now finished running in my 3.8 engine and started to open it up a bit on occasions.... I have done quite a bit to the engine.

Not to nit-pick, but if what you've done includes new rings (especially new chrome top rings), I would say you haven't finished running in. I have a friend who had a 3.8 E rebuilt by an American V8 specialist who did bad work and gave bad advice. The upshot was my friend's E was a smoker and drank oil, because he babied it for a couple of thousand miles and the rings never bedded in. I was dubious that much could be done given the distance he'd already done (may have been closer to 3000 miles) but I told him to thrash the thing to the red line and drive it as hard as he could as often as he could.

Transformed the car and saved him a rebuild for a hone and new rings.

Yours sounds as if it has been under-worked if you're only now venturing in 4000 rpm territory and it's not enjoying things...?

[andrewh]

Not on an SU it's not! It just drops the jet down a bit. It isn't a 'choke' at all, it's an enrichener.

Ah, yes of course, in which case I shall try that forthwith.

Peter, I have not been to gentle with it, I assure you. And I doubt the bores are glazed. Its a rolling road job I reckon. Rob Beere thought that UOs would be fine but it may need a bit more fuel so worth trying the richer jets.

So if we are in the business of recommending rolling roads tuners, anyone that comes with good authority?

[JagWaugh]

Bungs and sensors on each corresponding carb branch would be the best DIY instrumentation, but even a tailpipe test machine will give you a reasonably good picture of what is going on during a steady state road run.

We've got an old Bosch tester which indicates CO and HC. We screwed a 12VDC-220VAC invertor to the side, and run it off either a battery pack, or from the onboard battery (many of the cars we work on haven't got a cigar lighter, or are positive earth). It only takes a few minutes to fit, including duct taping the hose to the body and feeding it in through the passenger's window. We also fit a pipe clamp around the tailpipe and sensor tube clip to ensure that it won't come out.

The exhaust tester came out of a larger test rack which also included a scope. iirc the whole rack was something in the order of 80GBP.

You'll still have the 3 to two (or two to one) problem, but this would let you narrow your needle selection down to just a few possibilities before you pay hourly for the rolling road.

[Jaglex]

I fully agree with JagWaugh (as usual). Follow his proposal and you'll get your mixture right. And, please, let us know which needle you choose in the end.

I don't agree with most the comments concerning the 123.
I have one since quite some years and covered more than 30.000km with it without any problem despite using the "usual" leads and the old coil. (OK, I admit having my old dizzi in the boot when doing longer trips - just in case...)
The advantage of the programmable 123 is that you can freely adjust the curves and that you can switch between two curves while driving. The latter should be of great help to come closer to the best curve for your engine.
One problem may be that you will have to hear or feel, when the engine starts pinking. I don't know about a "pink-sensor", that can be mounted to our XK old engines.
Happy tuning!
Alex

[Hugo]

Most drivers come equipped with a pair of 'pink-sensors' - one stuck to each side of the head.
I have no direct experience of the 123 system, but from what I've read, they seem to work well when they work, but statistically quite a high proportion of people seem to have had issues with them, and most people seem to carry the old points distributor as a "just in case".

[andrewh]

I was down at CKL today and spoke with Chris Keith Lucas about it. Like the rest of us, he has experienced troubles with the 123, but when they work, they are a good thing. He believes that the issues with them have largely been ironed out. Interestingly they also have a distributor calibration machine, and can re map and existing distributor if the need arises.

As an aside, CKL is nowadays a seriously impressive place to visit, and I counted 3 or 4 original D types and I understand XKSS was in bound. Quite a few E types, and of course the XK120s , 140s etc etc .

[Jaglex]

@Hugo:
I heard pinking at lower RPM, that came up quite often with 97 and lower octane petrol until I changed to the richer needles after fitting the tubular manifold with the big bore exhaust and the high flow air filter.
But I never heard pinking at higher revs. Instead I heard this to be difficult to hear. As high speed pinking can cause big trouble I wouldn't rely on the pair of sensors that came with my head.
But I'm no expert in pinking sensors, so please correct me if I'm wrong.
Alex

[JagWaugh]

@Hugo:
I heard pinking at lower RPM, that came up quite often with 97 and lower octane petrol until I changed to the richer needles after fitting the tubular manifold with the big bore exhaust and the high flow air filter.
But I never heard pinking at higher revs. Instead I heard this to be difficult to hear. As high speed pinking can cause big trouble I wouldn't rely on the pair of sensors that came with my head.
But I'm no expert in pinking sensors, so please correct me if I'm wrong.
Alex

I guess you could fit a knock sensor on a stud somewhere, but you'd probably need some electronics to process the output - they aren't like a self contained switch, at least not the Bosch ones fitted to Alfas. I know this from having spent many hours with a scope trying to make sense of the signal on Alfa Turbo engines - and those were the correct sensor for that engine.

I'd say you'd probably be better watching the Lambda and erring a bit on the rich side.