4000 rpm limit 123 distributor

[Grant]

Hi All ,
I know there is a lot on here about 123 distributor and I’m regretting buying it , not because it’s a bad bit of kit but because of the resistance you get from the older mechanics when you try and fit it , they just seem to blame it for everything,
So here we go
I have just swapped from strombergs to Su , the “classic car doctor” I used was just not up to the job he did not seem to understand reading the instructions on the 123 may help and although he managed to set it up 8 degrees before ,but he seemed to do it in his own way rather than following the instructions and when he left she was running very lumpy and he was blaming the Bosch plugs I had in there , on his recommendation I fitted champion ones , and decided to get her turned on a rolling road , when I get there I expanded it all the guy checked the timing and said it was ok .
He then tuned it very nicely but cannot get it to rev above 4000 rpm it just dies , he said the curve was good and strong but at 4000 it just drops off .
I did my own tests on the way home and it seems to go well over that in all the other gears , but just drops off in 4 th any ideas ?
1969 USA ots
And I’ve put the recommended Bosch coil on ,

Thank you in advance! ( no pun intended ) :-)

Grant

[Tom W]

That’s frustrating.

Which version of the 123 do you have?

What total advance did you end up with in the end following the rolling road session?

Finally, are you sure the rev counter is correct? RVI tachos don’t always work properly with the 123 (or other electronic ignition). Hopefully the rolling road used an independent method for measuring the rpm, and didn’t rely on the rev counter.

[Grant]

Hi Tom
Sorry , there is always one thing you forget to put :-/ it’s the Bluetooth one , I stupidly for got to save it or screen shot it at the time , I have one from before which I will put here , and I’m not aware of him touching anything ,
I will attach the read out , if I can
. Just put in resistance plugs as I’ve seen that mention but waiting for rush hour to blow over before I take her for a run,

Thank you

Grant

[Grant]

Hi Tom
Do you have the Bluetooth one ?
Would you happen to have the picture of your 123 curve ?

Thanks again

Grant

[christopher storey]

There is something very odd about the advance curve, in that 29 degrees full advance ( including the static 9 or 10 degrees ) should be achieved at 3600 engine rpm, with 25 at 2500 rpm, whereas you have 24 and 16 degrees at those speeds respectively i.e. you are significantly retarded . Secondly, there is this very odd falling off a cliff at 3950 - 4050 rpm, which suggests that in 100 rpm the torque diminishes by about 12 - 15 or so percent. This curve is way off what one would expect, and may be the reason for the inability to go beyond 4000rpm, because the gradient of the curve suggests a virtual complete shut down at 4000 rpm .

However, I note with a sinking heart a reference to modified UM needles - who has modified these and how - because fiddling with the needles with a needle file, particularly on a 3 carburetter car - is a recipe for disaster

[Grant]

Hi Christopher
I should say I know nothing about distributors or timing but

That does not surprise me at all , as When I tried to help the guy set it up by reading the instructions and found the green light for him etc it did not work at all but I have no way of knowing if he had the engine in the right place to start with .
I did notice that when he set the static timing and installed the distributor and it was turned until the green light came on the arm did not point to the 1 on the plastic cap ? When it was lined up to clip on ,
Then he kept fiddling around until it finally worked
However the guy at the rolling road seemed happy and he did appear to put a timing light on it , but I was not allowed to be there when the engine was running .

Yes I noticed the thing about modified um jets I have no idea about that as I thought they were just standard and was not aware of any modification, I will call them tomorrow and see what he meant .

Thank you for your reply

Grant

[Tom W]

My car has a Jag123, with the preset curves. The settings I use won’t be suitable for your engine, as I have Webers on my car. I think there’s a few Bluetooth curves uploaded to the knowledge base on the forum.

I agree with Christopher, I don’t think your advance curve is right. I’m also not sure your distributor is timed correctly. Going from the S2 workshop manual, the maximum advance should be 29degrees crankshaft, at 3600rpm, for a 9:1 engine. There’s a bit of tolerance allowed in the factory figures. Looking at the lower end of your curve, there’s no advance at all. This suggests the distributor might have been installed with some idle advance. If that’s the case, you need to know how much, to add that to the numbers on the curve. If it has been installed with some advance, then your car could be over advanced. I’d check by putting a timing light on it and seeing what you actually have at idle.

If it is way over advanced, you could do some damage by trying to thrash it over 4000rpm.

I don’t think installing the distributor with advance is the best way with the tune version of the 123 though. The instructions are a bit vague, but I think it’s best set to TDC, then all the idle advance, and everything else is controlled in the app. The figures shown in the app are then the actual advance figures your getting at the crank.

A good starting point for a curve would be to copy the one in the factory workshop manual.

[mgcjag]

Hi Grant....to be honest a 123 tune or any distributor is not the sort of thing to be playing with if you know nothing about timming......you really need to take the car to someone who know how to set this up....this is a curve that was posted on Jag lovers...note timing is set a 0 deg (tdc)Steve

[Grant]

Hi Tom and Steve
thank you for your replies ,
Tom ,can I just confirm that at the moment the diz was set with the bottom marks static at 8 btdc, which I will try and check (for the first time on my own tomorrow), by going for a drive to get her up to temp then jack up which stands etc and get the light on it connected to the plug nearest the screen ? No 1 ? and hopefully it should light up at 8 btdc if this is the case , can I loosen the distributor a little and rotate it to remove that 8 degrees?
I know this sounds a bit obvious to you guys but I don’t really have anyone local that I feel I can call for this ,
And you are saying that the 29 degree on the app at the moment is plus the 8 already on there from static so could be nearer 38 ? Which is too many ?

I hope I have not bored you all to death ,

Thanks again

Grant

[Tom W]

Yes, if you have 8 degrees BTDC shown on the crank pulley, you have to add that to what the app is showing to get the total advance for any given point. Rotating the distributor anti-clockwise will reduce the timing, clockwise adds to it. Rotating it 4 degrees will change the timing by 8 degrees on the crank.

You can use either plug 1 or 6 to set the timing. Either works, so use whichever makes it easier to get the leads on the timing light to reach without catching them on the exhaust or drive belts.

Setting the timing by rotating the 123 dizzy is fiddly as you can’t see the timing marks at the point you move the dizzy. Alternatively, you could set it with the engine off and at TDC using the LED, as per the instructions. Then check with the timing light afterwards.

Once you’ve got the dizzy set to TDC, you’ll need to modify the curve on the app to add back the idle advance.

A final point to note, your TDC pointer might not truly be at TDC. The pointer is slightly adjustable, so it’s best to confirm exactly where TDC is before starting.

[abowie]

I know nothing about the 123 but just checking that the unit doesn't have a built in rev limiter that someone has accidentally set to 4000 rpm.

[Grant]

Hi Andrew

No I do not think so , both. My self and the guy at the rolling road 'had a look but we could not find anything like that .

Thanks for the thought

[Grant]

Hi Tom ,

Sorry I had not seen your answer , thank you once again for a really informative answer,
I will study it properly in the morning and give it a try ,
I will let you know how I get on ,

Thank you

Grant

[Tom W]

One final thought. Can you post a picture of the current Bluetooth curve before adjusting anything, and also check, but don’t adjust the idle timing. You mention the screenshot was from before the rolling road session. If the rolling road have changed it, you may be about to adjust what’s already right.

[mgcjag]

Just to add after re reading the original post....you said a drop off above 4k revs on rolling road....but you tried it later and you could get above 4k in lower gears.....you could possibly have a fuel problem......so worth looking at...especially as you changed from strombergs to SU,s......was the car running ok after this change or did you change the dizzy st the same time......PM sent.......Steve

[christopher storey]

Can we try to clarify this. The static timing, and the mechanical advance, have nothing to do with each other except arithmetically - the mechanical advance is added to the static advance to give you a total advance which you can see with timing light. . For a UK spec 1969 car, you want either 9 degrees static BTDC for an 8:1 compression car, and 10degs BTDC for a 9:1 car ( yes, it is that way round ! ) . Then, once the engine is running , you want some additional advance to start at about 1050 rpm , increasing to about 13 additional i.e. 22/23 btdc at 1600 rpm , and to about 15 additional at 2500 rpm = 24/25 total , and about 19 degs additional i.e. 28/29 BTDC at 3600 rpm and staying at that level through the rest of the rev range . If you want to see the exact factory advice about this, it is in the knowledge base which contains the workshop manual at section P . Note that 4.2 settings are different from 3.8 settings, and that for the 4.2 cars the settings are at pages P.X s1 and P.Y.s.3 ( this last may not be on this site ). Note that these settings in the manual are for distributor degrees and rpm which are half of crankshaft degrees and rpm

PS One further trap for the unwary is that ( if one is fitted ) it is very common for the external pointer which shows the advance with a timing light to be way adrift , often by as much as 5 or more degrees . The more reliable TDC timing mark is to be found on many engines as an aperture on the top left of the bellhousing (to the rear of the dipstick ) which reveals a mark at TDC . Each tooth of the ring gear represents 2.75 degs of crank movement

[Tom W]

I think the confusion comes with the 123, particular the tuneable ones, and how setting those relates to traditional distributor nomenclature.

Arguably there is no static timing with the 123, because you can’t measure it statically in the conventional way. What there is though is a reference point. This is when the LED illuminates, but it doesn’t indicate when the spark occurs. It just indicates a known point the distributor measures from. For the tune versions, this should be at TDC.

The idle advance is then set electronically in the software. That way, what you see on the app is what the engine’s actually doing. For the E-type on SUs the idle advance is the same as the static advance quoted in the manual, because the mechanical advance hasn’t started at idle speed. Similarly, the mechanical advance is applied electronically.

[Grant]

Hi again Tom, Steve , Christopher,
thank you all for your replies,
Tom your first one yes I will take a picture of the curve on the app as it stands etc before I begin,
and Steve thank you for the pm I will do that later,
I will have to have a good read of the other posts later and let them sink in before I come back to you guys , Im hoping to do it later today.but the rain may stop play.

Thanks

Grant

[Grant]

Hi Tom, Steve ,Christopher

Ok so here are the pics of what I have at the moment .
The first 2 are of the 123 when I have just switched the ignition on .
Then the follow are the dashboard at the various numbers Christopher mentioned , ie 1050 rpm1600rpm etc,
What I noticed was that it did not stop at 29 (as per the first picture ) or 37 if you assume it has 8 degrees static which was I was told and what the rolling road guy confirmed on the top of the sheet had been added it just kept on rising .?
Sorry it seems to shuffle the pics I’m not sure why , I also noticed on the 4000+ revs it does appear to be 38 but this was just when the pic was taken it was still climbing with the revs and should be plus 8 static from what I understand .















Thank you again

Grant

[Grant]

I have just placed the figures on a single graph the way I understand it