Does anybody use one of these distributors and, if so, which curves have you used and how did you find them?

For the record, I fitted the 123-JAG version in August 2016 and initially used curve B. This led to pinking at 2,000rpm and above, so I switched to curve 6. That's fine up to about 2,500rpm, but pinks somewhat thereafter under heavy load.

My 3.8 engine has a CR of about 9:1 and I use 97RON Super Unleaded. The original spec was 8:1 but I think through skimming over the years and perhaps the new pistons fitted during a rebuild in 2015, it now seems, from a compression test, to be about 9:1.

I set the timing to 4 degrees BTDC (the manual says 5 BTDC for 9:1).

So, I'm now considering alternative curves (it seems curve 1 or 3 would be the next one to try) and/or further retardation of the timing.

Does anyone have any experience to offer on this, esp on 9:1 engines?

 

Welcome! I have no experience with these distributors but hopefully someone here does.

 

I looked into 123 for my 3.8S, but went with Mallory unilite.

If you at look the notes on the attached spread sheet, it appears to me that 34 degrees at 3600 RPM is the max you want to go to. That would be the "0" curve. with timing set at 10 degrees static.

Looking at the distributor curve graphs, you see distributor 40617A being the most refined curve for the 3.8-4.2 XKE engine with the triple SU carburetors (pre-emissions tweaks). With out a racing setup, this would be the best curve to emulate.

Rgds David

 

Start with curve 0 then if no pinking go to 3, if still no pinking go up to 4 and 5, if you get pinking at 3 try 1 then 2.

Check the all in advance with the Vacuum detatched this should top out at 3600 rpm and should not be much over 32 deg but a max of 34 deg with curve 6, if it's higher you probably need to retard the static a little. How have you set / checked the air fuel mixture ?

 

I fitted a 123 to my E Type 4.2 and decided to use Curve 2. I did not have any pinking problem but it may just be that I did not rev it that hard. Attached is the summary I used in making the selection.
It is obvious that these distributors give excessive advance at high speed even using the lowest setting (Curve 0).
As they say YMMV

Bruce M

 

Thanks everyone for your suggestions.

I think I will start with Curve 0, because if that one still gives me pinking, none of the other curves will help.

The needles and jets are five years/7,000 miles old; the piston springs are within spec. I set the mixture using Colortune and a Gas Tester to give 6%CO at idle. The plugs look the right colour.

David84XJ6, how did you get on with the Mallory Unilite?

 

Doing a bit more digging, if you buy a modern 123 ignition, you can easily customise the advance curve and the vacuum curve with up to ten points each.

I downloaded the 123\TUNE program to try it and was able to replicate the Jaguar curve easily enough.


123\TUNE advance customised for E Type


Bruce

 

Thanks for going to all that trouble, Bruce. And it's good to know it can be done. If I don't get any joy from Curve 0 (now applied but not tested yet), the 123-TUNE is likely the way to go.

Thanks again.

 

You should check the all in advance at 3600 rpm to make sure the distributor is actually doing what it is supposed to and it not "out" in the first instance.

What needles are you running ? I am assuming this problem has occurred only after changing to the 123 distributor and you had no problem before so can rule out fuel mixture ?

 

Yes, I will check the all-in advance, but will have to figure out how and where to make suitable markings on the crankshaft damper first. And also need to wait for all the neighbours to go out.

The needles are standard. It has pinked since I acquired and restored the car in 2014 - before I put the 123 distributor in. As I said in my question, the car was manufactured as 8:1 CR and had the 8:1 Lucas distributor. Either through head skimming or the decision of the engine builder, it's now 9:1. I think it's much more likely to be ignition than fuel.

I will report back on Curve 0 after a run out in the sunshine tomorrow.

 

Bruce,

Looking at the "Tuned" advance curve going from 0 to 29.4 degrees advance, it appears for the 3.8 engine, a 5 degree static setting would be right???

My original 1965 3.8S engine called for 29 degrees at 3000 RPM with 98 octane fuel. I went to 30.5 degrees at 3000 RPM with 91 Octane fuel.

The the original 1965 distributors were pre-smog distributors 40617A (150S & E-type)- 40886 (3.8S). The 41060A, 41207 and 41322 were emissions models with performance downgrades to accommodate emissions targets.

If you can tune the 123 to pre-smog curve you should have maximum safe performance.

See attached summary

 

Most 3.8S Engines had the 41063A distributor. They used TL needles.

Static timing was.

 

"If I don't get any joy from Curve 0 (now applied but not tested yet), the 123-TUNE is likely the way to go."

If you go with the special tune, it appears that the 4 speed transmissions used a 7 - 14 - 8 vacuum advance curve and the automatics used
a 5 -12 - 8 vacuum advance curve.

The Mallory was great, with adjustments to max advance and different springs for quicker or slower spool up. You can't get parts now, company sold out; (Vacuum advance failed) so I retrofitted a compete distributor and amplifier off a XJ6 S3, with a LU-BD198: 40,000 Volt 0.8 Ohms Coil.

Looking forward to your test results. Rgds David

 

The vac advance should have no relevance to the pinking issue it only really comes into play at cruise or de-acceleration.

The distributors for the 9:1 comp engines were different than standard, and they require less advance, retarding the engine to stop pinking if taking the overall advance too low is not the only or necessarily the best way, too little advance will make the engine sluggish, so the air fuel mixture at higher revs should be considered by possibly changing the needle from a TL to a C1 (or maybe even richer in the midrange). I would look at total advance and also fuel mixture at 2500 rpm when the issue is presenting, the pinking can be eliminated by retarding the timing, but loss of power may be the result if the fuel mixture is not addressed.

 

Hi again everyone and thanks for your further contributions.

Early indications are that Curve 0 seems to have solved the pinking problem, although there wasn't much clear road where I needed it today.

I set the static timing to 10 BTDC as suggested in the 123 manual. And that seems to make it nice and responsive below 2,500, but still gives good response at 3,000. Haven't gone any higher, yet.

I still get a weird high-pitched shrieking noise on hard acceleration as it comes up to 3,000rpm, but don't think it's pinking. Fan belt slipping, maybe, or perhaps the rev counter generator. Who knows. I will create another thread if I can't get to the bottom of it.

Thanks again for all your help and there is some really valuable info here for future browsers.

 

Good to hear you are getting positive results on preliminary test ride!!!

Here is quote from Jag Lovers about Mark II tuning: "The Jaguar spec for SU Carb dampers is 20 wt engine oil, ATF is closer to 5 wt. Heavier oil makes the acceleration mixture richer, which usually lets you run a bit more timing for a specific fuel. All XK’s are knock limited and can use more timing than most pump fuel octane will allow"

Rgds David

 

Hi again, Dave

Yes, I do already use the SAE 20 oil supplied by Burlen. Though not sure how well it copes with the phenomenal temperatures under my bonnet.

 

Great result, don't get us started on SU oil weight and temperature, one day Glyn will actually do a test/check on the carb temp, everyone assumes it will be high due to engine bay temps, but doesn't take into account venturi cooling effect, Glyn has mooted doing a physical check, maybe if he gets time he will get around to it as it would be very interesting. (little poke there Glyn ! )

 

The cooling effects of fuel vapourisation & the venturis is substantial in the carburettors . (e.g. carb icing was common with the Austin Mini & SU carbs. Icing used to seize the dampers under the right conditions)

Yes ~ wish I'd done this testing in our labs before retirement with all the right gear. The carb dampers run far colder than you would ever imagine. Not below freeing point beyond the venturi like certain Mini's & some VW products with Pierburg carbs it would seem.

Speculation that carb dampers run anywhere near underbonnet temperatures is definitely not so & flawed thinking on many forums.

I've caught temperatures beyond the venturis at 6 deg C with a Fluke touch thermometer after a short run with no aircleaners. This is by no means scientific or necessarily accurate.

TJ ~ I need to find a way to rig up decent thermocouples & try & record temperatures in differing conditions to get some decent & repeatable plots. The closest gear to enable this is in our labs in Belgium. Not getting there any time soon. Sasol could do it by why should they for me.

Very early indications are to stay away from high viscosity, low VI mineral oils that thicken substantially as temperatures drop. Live with SAE 20W ~ preferably high VI synthetic & depend on that level of damping to slow initial piston rise to increase depression over the jet to give the accelerator pump effect.

Sorry I can't be more encouraging but I have other priorities & some hurdles to overcome. In retirement I simply don't have access to what I'm used to having. I don't expect to have answers to this anytime soon that I would put my name to.

People are welcome to mess around taking carb temperatures & draw their own conclusions.

All I'm prepared to say is that early indications are that the carbs run far colder than many might think.

I say use high VI synthetics because they change less in viscosity for a given change in temperature than their mineral counterparts. This should give SU's more consistent performance.

EDIT: What I would like to do is run a car on a Dyno with controlled inlet air temperature, known humidity/air density etc etc. at different loads & engine speeds.

 

Thanks for the reply Glyn, your past life adds weight to this.

It's not high on any priority list, just suffice it to say, as you have that carb temps are far lower than most people expect.