pre-programmed curves on 123 ignition - help please?

[mgcjag]

Hi Tom....why is your car idling at such low revs......iv never actually looked but seen quite a few 4.2s with webbers idleing at what i would think was higher.....that would sort you map problem or just add mechanical advance......Steve

[Tom W]

The car idles smoothly at around 750rpm when it’s warm. When it’s cold it idles lower as there’s no mechanism on the Weber carbs to increase the idle speed. If I increase the slow speed running setting, it will increase the RPM at both hot and cold idle. I’ll also start exposing the progression holes if I adjust it too high, which is not desirable. Webers seem to need more low speed advance, so loosing advance doesn’t really help the idle speed and it becomes a vicious cycle. Ideally I’d have a curve with a dip at idle speed, so a reduction in RPM increases the advance slightly, giving a more stable idle.

I’ll do a bit more experimentation using the tune function on the app to try and find the optimum idle timing. If I can get it to idle above 500rpm when cold, I think I’ll be able to install the distributor at TDC and programme everything in the app.

[John ball]

Tom, I assume your engine is tuned up, as the reason you have decided to use Weber’s instead of SU’s ? Surely the only reason to use Weber’s is for more power, combined with other tuning mods. Also they use more fuel.
I don’t think I ever see a Weber equipped car idling at 500rpm. Normally more like 800rpm. Certainly, full race or fast track cars have a cam that really does not like low idle speed.

[mgcjag]

Chatted to a couple of mates last night running webbers on 4,2 engins with 123 bluetooth set at tdc.....no problems starting or cold or warm idle.......the suggestion was the webber setup isnt correct either idle or mixture or both......you mention no choke..can you not connect up the manual choke...the guys iv spoken to have the choke connected...Steve

[Tom W]

The car is on Webers because that’s what the previous owner fitted in place of the original Stromberg setup. If it were on SUs, I likely wouldn’t replace them with Webers, but I’m not about to swap the Webers for SUs. Apart from a tubular exhaust manifold, sports exhaust and the 123 distributor I think the engine is otherwise standard. I’ve not pulled it apart to see.

Mixture and idle speed on the carburettors are already set correctly. This is a timing or more specifically a 123 problem. With the pre programmed 123 I previously had fitted, timed to 12 degrees at idle, the car would start and idle, albeit with a lumpy and lower idle speed when stone cold. The idle RPM would increase and the idle quality improve as the car warmed up. This is to be expected. The same can be experienced on an SU equipped car if the choke is pushed in before the engine is properly warmed up.

The car behaves the same with the 123 tune installed with 10 degrees static timing and 2 degrees programmed into the app. In this instance the 123 isn’t able to drop the timing below 10 degrees and the car will still start and idle from cold.

I only encounter the problem when I install the 123 at TDC and add all the idle advance in the app. I might have asked for 12 degrees in the app, but at 500 RPM it gives zero, and the idle speed drops further and the car won’t run. It’s not a Weber problem per-say, more a scenario that’s only encountered with Webers as they lack the fast idle control of SUs. Im sure if I installed race cams such that the engine then needed 1000rpm+ idle speed I’d probably avoid the problem there too, but they wouldn’t be so suitable for a road car the rest of the time.

I installed the tuneable 123 so I can add the appropriate amount of ignition advance lower down the rev range that’s lacking in the pre-programmed curves. But it seems with these things nothing is as straightforward as it ought to be, and fixing one problem brings with it several others to solve.

With the 123

[John ball]

Tom, how do know on the pre programmed version the advance curve is too low as you stated. I thought it only gave a few set positions, like idle and max advance. Have you tried all the positions on the pre programmed version as an experiment?

Tomorrow, I will contact 123 in Holland and ask them if their system has any disadvantages or advantages with the static at TDC with the curve starting at 10 BTDC or Static at 10 BTDC and curve appropriately lower ???

But, as I said before, when I tested both ways I could not feel any difference in the running of the car.

[MarekH]

You sound as though you'd like to balance the idle speed via additional advance when the engine is cold as your settings are already fixed for fuel and air regardless of temperature.
kind regards
Marek

[Tom W]

I plotted all the curves for the pre-programmed Jag 123 fr the workshop manual. They each have a start point, mid point and end point, but it turns out the mid point is just a point half way between the start and end points. So each curve is actually a straight line. When overlayed over the original Jag curve, the advance on all the curves is lower through the early rev range but ends up higher overall. Malcolm did some tests earlier in this thread on his Jag 123 plotting advance at different speeds with an advance timing light, I’ll have to draw his readings too.

Either way, with the curve I’ve now programmed, following the factory 4.2 curve, the car is more responsive low down.

That’s sort of right Marek. Settings for idle speed and mixture are fixed irrespective of temperature aside from constantly blipping the throttle until the engine is warm. I’m not looking for a different advance value when cold to warm. What I’m getting, which I need to avoid, is a substantially lower advance value at cold idle rpm vs hot idle rpm. Ideally I’d have a couple more degrees at a lower RPM value than the warm idle RPM to create a more stable idle. I can achieve all this with the distributor installed at 10 degrees, but so far not though the app alone when installed at TDC.

[mgcjag]

Hi Tom...i asked in my previous post about choke...do you have this disabled on your webbers...have you tried connecting it up it would improve your cold start/idle..Steve

[Tom W]

Sorry, I missed the comment about the choke. It’s not sensible to connect the choke on Webers. Apparently they’re not particularly reliable, and if used regularly can lease to either air leaks or fuel leaks. Not every model of weber comes with them, and blanking kits are available to remove those that have started leaking. It’s not necessary if the ignition advance is correct either. A couple of pumps of the throttle before trying starting is enough to get the car to start from cold.

[mgcjag]

Hi Tom...well as i mentioned the guys iv chatted to dittched the 2 pump method and connected up their chokes...cars run well on cold idle....must at least be worth you trying it......but the 123 instructions that iv seen do say to set your 123 at your static point......Steve

[John ball]

Hello Tom and all, I have been away for a week, so late reply. I have had various emails back and forth with
123 office in Holland. Contrary to comments they said to me some years ago, now they are saying it is better to set the system to start at the position of 10 degrees BTDC. But, that does mean that taking the 10 into consideration the max advance on the program curve would be for example 24 not 34. On the screen it states crankshaft degrees, but really it is only what you have set as the static plus what you have programmed, so not necessarily the true crankshaft curve and max. It obviously does not know what you have set as static.
Whereas setting it at TDC you can set the whole accurate curve and the system with the engine running shows the correct figures. But they have stated in their email to me that there is NO advance below 500rpm, thus the reason the car may be harder to start with set at TDC versus set at 10 BTDC. I don’t think their system is very clever, as they should have on the screen a 0 rpm point where you can set 10 BTDC, then you can set it up as I originally suggested to give true crankshaft degrees on the screen!!??

[bitsobrits]

Virtually all ICE will be easier to start with initial timing at TDC than with any amount of advance before TDC. Which is why all the early automobiles had advance/retard levers to allow the timing to be retarded to TDC or after for easy starting, then manually advanced once running (and of course allowed for additional advance at higher engine speeds or when under light throttle).

I set my up the initial timing of my 123plus units (one in E type, one in 308 Ferrari) at 0 (TDC) and it all works as planned. These are brilliant devices, but the factory information is less so.

[Tom W]

Hi John,

You’ve confirmed what I thought was happening then. I’ve not had a chance to do any more tests yet, but I think I may have to leave it installed at 10 degrees.

I was expecting the engine to be easier to start with lower advance at cranking. Whilst it is easy to get it to start, it’s not easy to keep it idling without massaging the throttle constantly.

I think it will work properly when set at TDC if you have an engine where the revs don’t drop close to 500rpm or lower.

It would be useful if there was a function in the app to program the static setting, so the figures displayed on the dashboard and the curves were displayed as correct crankshaft degrees.

[John ball]

Steve, yes I was aware of the fact that many prewar cars are started with the lever in retard then advanced once running and driving. I wonder where the retard takes the timing to is it TDC or even before or after ?
I have never heard of anyone saying what the degrees are ? Or even how advanced in full advance ? But, am I not right in saying that with an original Lucas distributor that has springs and weights that do not advance at starter motor speed, then you would still set your E type at 10 BTDC if you did not have a 123 system ?

[Tom W]

From the data in the 3.8 workshop manual, the original mechanical distributor doesn’t apply and advance below 650 rpm, and the idle speed is 500rpm. So timing at cranking is also 10 degrees.

[Tom W]

I’ve just updated the 123 app on my phone. I can’t remember when I last updated it, so don’t know when this came in but it looks like there’s now a function to add a static advance value in the app. This would appear to solve the problems we’ve been discussing related to whether the distributor should be set at TDC, or at some other static advance value. I don’t think it modifies the curve itself, but does change how the live advance values are displayed in the dashboard. No more mental arithmetic, and what’s measured on the engine with the timing light should match what’s displayed on the app.

[John ball]

Hello Tom, I have looked at my Bluetooth 123 and agree with you, it appears to have this update. I wonder if this is because of my calls and emails to them in Holland. But, I have read the wording when you touch the orange circle exclamation mark on the curve page when you edit a setting and find it extremely difficult to understand exactly what they are saying.
I ran the car as set up with timing set at TDC and the strobe light showed 15 degrees at 900 rpm as the program curve page. I have the program page showing 10 degrees at 500 rpm and 650 rpm.
But the dashboard was showing near 25 degrees. I don’t understand where I have gone now.
I note under the settings page there appears to be a new line that says ‘ include static advance’ which was clicked on without me doing anything. I would be very interested to know from your experiments and settings what you find. I am wondering if their update is a complete “red herring”.

Maybe another call or email to them will necessary ??!!

[Tom W]

Hi John. I did some experimentation yesterday. I have my distributor installed at 10 degrees and I tried with zero degrees programmed in the curve at idle on the app. With the “Static Advance” setting on the curve set to 10 degrees, and the “include static advance” the dashboard shows 10 degrees at idle and the timing light shows 10 degrees on the crank pulley. So for checking everything on the dashboard, this works in an intuitive manner.

The numbers I have programmed in the curve are all still crankshaft degrees, and they’re the amount of additional advance applied relative to whatever the starting point is. I didn’t have to change anything on the curve. This setting is purely so the dashboard knows what the static advance is and can now perform the calculation to show the total crankshaft advance.

If you have your distributor installed at 0 degrees don’t use it as the dashboard will display incorrectly. If you have some static advance in the distributor installation, using this setting will allow the dashboard to display correctly, but it doesn’t make any difference to how the car runs.

[John ball]

Hello Tom, sorry to sound so stupid, but just want to confirm if my numbers come to the same answer as you but by a different route ?

To summarise your setting below, then followed by mine.

Distributor set 10 BTDC
0 in the curve at idle on app
“Static advance” 10 BTDC
“ include static advance” button in settings ON
Dashboard shows 10 BTDC at idle
Timing light shows 10 BTDC at idle

Distributor set 0 BTDC
10 in the curve at idle on app
“static advance” 0 BTDC
“ include static advance” button in setting ON
Dashboard shows 10 BDTC at 650 rpm and 15 BTDC at 900 rpm
Timing light shows 10 BTDC at 650 rpm and 15 BTDC at 900 rpm
Note: my car idles best at nearer 800 rpm, probably due to camshaft.

Maybe, this programming is the same answer but yours is more sensible ?

FYI info my curve is
10 @ 500
10 @ 650
15 @ 900
23 @ 2300
28 @ 1700
32 @ 2600
34 @ 3000
34 @ 8000

Vacuum
0 @ 14
33@ 14
57@ 12
70@ 5
75@ 0
200@0

This vacuum curve was recommended by 123 email.

Please can you tell me your vacuum curve.

Thanks John