123 Ignition Timing

[studioPaGoNa]

Dear All

Please allow me to ask your help or guidance, although similar subjects were discussed in this forum.

I am struggling and tired for fixing the 123 Ignition timing on my 1968 280SL USA version. Just for your information, the exhaust emission function is disabled and I use a regular gasoline with 90 of octane in Japan here. The engine oil is 20w50. I renewed the whole ignition system such as spark plugs, spark wires, coil (Bosch red coil). I believe that I completed the linkage tour properly. I use Gunson CO tester to confirm CO in an allowable exhaust range during the adjustment.

Prior to setting the 123 Ignition, I forgot to check the ignition timing on the original 051 distributor which was installed by the mechanics.

In terms of the 123 Ignition, I preset the advance curve as “8” as normal. At first I set 4 degree BTDC without vacuum at idle so as to be 30 degree at 3000rpm but the engine immediately stalls with vacuum connected. Then I advance, say to 10 degree BTDC at idle without vacuum (1 degree BTDC with vacuum connected) so that the engine is running fine in a warmed normal operating condition, leading 37 degree BTDC at 3000rpm, but I found that the engine tends to stall during the warm up process. I further advance to 16 degree BTDC without vacuum (8 degree BTDC with vacuum), the engine is running fine in any stage, in which pinging is observed in rare cases (I tried 100 of high octane gasoline and it is confirmed OK). It seems that an optimal setting would be between 10 BTDC and 16 BTDC. I think that this is too much advance. I would like to clarify that it is an acceptable range or it requires adjustments on other area?
Thank you for your advice in advance.  Koki

[Jonny B]

There is an in depth discussion of the 123 ignition in Pagoda Notes, Vol3 No 4. This is accessible through the premium content (for full members).
Click on the "Technical Manual" tab at the top of the page, then scroll down a bit to the "premium content" link. Again, scroll down, and there is a link for Pagoda Notes. You should be able to get the article there.
Also the search function should help to find other information on the 123 set up.
Good luck and welcome to the forum.

[Cees Klumper]

The only thing that caught my attention in your description is that, at some setting, the car runs good when warm but stalls during the warm-up process. Mine does that as well and I don't believe that is due to the ignition setting (although I do have to report that I also have a 123 ignition, and couldn't be happier with it). I intend to add a shim to the fuel injection pump, in order to enrichen the mixture dueing warm-up, just to see if that cures it."For what it's worth", good luck with getting it straightened out.

[Atazman]

I have the 123 ignition system as well.  Right now, I'm running with basic timing at about 8 Deg. BTDC with the vac. line connected.    Thus, total advance should be 37 - 40 Deg. at 3000 rpm (not verified).  Attempted this advance to see if better fuel mileage can be obtained.  The car runs good without any pinging.  No problems through the warm-up stage.

i agree with the last post which suggested a fuel enrichment problem rather than ignition.

[studioPaGoNa]

All, thank you very much for your advices or suggestions.

Actually I learn lots through the premium contents and threads in the forum which really contains huge useful information.
The SL113 club is a very priceless facility for me surrounding by a very limited information and isolated circles here in Japan.

Talking about the 123 timing, I am relieved to learn that the timing at 8 degree BTDC with vacuum connected has actually been applied. 
Prior to such setting, let me study the shim issue associated with the injection pump at first so as to try it on my car, which make sense while I am not aware of it.
Regards, Koki

[studioPaGoNa]

I studied lots about WRD and Barometric compensator in the fuel injection pump.

First of all, I adjusted the ignition timing at 6 deg BTDC with vacuum connection in which the max advance is 37 deg BTDC.  I have still a problem at the warming up stage but it is slight. I need to extend the warming period of WRD. Is my understanding that removal of shims below the thermostat of WRD extends the warming period? Is it correct? I have one aluminum shim below the thermostat.

Next issue is how to improve my extreme bad fuel consumption which is about 7-9MPG in the street drive. I found that it is normally about 17MPG referred in the forum. In order to improve the fuel consumption,  I am thinking of removing shims under the barometric compensator easier than removing the oval shims under the air valve housing of WRD. My BC seems to be fine, judging that the length is about 22mm from the end of pin and the hex seat. I have currently 3 shims which totals 4.75mm, consisting of 2.0mmx2 and 0.75mm under BC.
So, I would like to clarify if it is usefull to remove the shims under BC in terms of improving the fuel consumption and how much a normal length of shims are in place under BC though there are different individually. 

Appreciate your inputs since I am confused at moment.
Regards, Koki

[Cees Klumper]

Dear Koki - My educated guess is that to add to the warm-up time one would add rather than remove shims under the thermostat housing.

For the barometric compensator one would remove shims to lean out the mixture over the entire range. But make sure there is not another cause of such poor mileage, such as a leaking cold start valve.

[studioPaGoNa]

Cees-san,
Thank you for your valuable advice.  Otherwise, I would have a big confusing about extension of the warming up period.
Regarding the CSV, I checked before that it was ok. Anyway, I will try all stuffs in this weekend.
Best regards,

[studioPaGoNa]

I tried to extend the warm up period but it is still not sufficient. The engine stalls.
The shims are totally 1.5mm in the slide valve at the moment.
I would like to know how much thickness it is generally. Here is not so cold at present and about five degree Celsius lowest.
Thank you for your input in advance.

[450sl]

Koki, are you sure you have proper vacuum available to the 113Ignition ? ; somewhere on this forum there is talk about a modified throttlebody.. or does this apply to only the later (280) version ?

[studioPaGoNa]

Thank you for your advice, 450sl.
I browsed most of threads relevant to the vacuum inlet for 123ignition and I understand the issue.
I believe that my vacuum inlet is correctly set up because the vacuum pressure is max at the idle and it drops zero when throttle is open.
Is it correct?