350 SLC 1972 troubleshooting

Hi Sylvain,

it looks like nothing is wrong with your distributor. Its rev change is within limits and its vacuum advance also.

BUUUTTT !!!!!!!!!!!!!!!!!!!!!!!!!!

Your throttle flap only has a retard vacuum connection as did all early 350 SL/C . When your distributor was replaced it was correct to only connect one vacuum line on your distributor and seal the other one. However it is now connected to advance input and not to retard input. Change the vacuum line to the other connection and be happy

Then you will have ignition timing of 0° at idle.

Hello Norbert

I haven't try it yet.
But i assume that the two pipe must be connected wich is not my case.

The one above wich is on every distributor is the retard, used mainly for idle.
It brings between 8 an 10 ° retard, as described in the mercedes document below.
It is consitent with my tests above.



for the distributor with two vacuum pipes :
0 231 403 001
0 231 403 005
0 231 403 009

the second vacuum pipe (below, the one sealed on mine) should bring 8-12 degrees advance at 3000 rpm.

I will try to plug the advance vacuum on my distributor. to see if it is consitent with the mercdes document above.

The big question is where should i plug the Advance Vacuum on the engine ?

As i understand the Retard Vacuum is plugged on the throttle body.


There is no other vacuum line on the trhottle body.




I have check the other vacuum lines on the firewall.
One is not used.


Maybe it is the place to plug the Advance vacuum.

Hello Volker,

you mean that the above connection is for advance
and the below connection is the retard ?
And mine was misplugged by a previous owner / mecanics ?



When the two vacuum are plugged there should be two vacuum pipes on the throotle body ?

Hi,

yes that is waht I mean and have also decribed earlier here

And I do not know why you put a Pertronix / Fullmax / Powerspark contact when you anyhow already have a transistor ignition system. Makes no sense. Most probably previous owner installed it due to his mistake on vacuum connection.

Check that he did not also change power resistors and ignition coil. Because that is another fake myth that you can then just remove power resistors and car will run smoother. Great bullshit you should not believe in.

Thank you volker,

you are more than right.

I have found the same document in english.


I will try it right away.

That is the problem with 40 years old car that have been maintained by poor skilled mecanics.
After that it takes you more time to identify and correct the issues created by them.

With the spares that came with the car, i had the original contact and condenser.
I will check the coil and may be go back to the original system.

Regards

Volker,

I just did a quick test with the vacuum lines plugged the right way.

I set the timing to 34° @ 3000 rpm without vacuum

@ 1500 rpm i have 18°
@ 750 rpm, idle, i have +2°

It is much better and consistent with the factory setting.
The engine is still a bit lazy at high rpm.

I tried with a little more advance, around 7° @ idle.
It is working up to 6000 rpm fine.


I will investigate why the factory setting is lazy.

May be it is the timing chain that is lengthen and change the timing settings.
I will open the camshaft covers to check the chain and guides.

May be it is related to the pertronix "upgrade".
I will check the coil and resistor values.

May be it is related to the switchgear. I am not very familiar with it and try to document myself on it's behaviour.

regards