350 SLC 1972 troubleshooting

I have check again my ignition timing today.


Try 1:
Set the timing to 34° @ 3000 rpm without vacuum.
@ 1500 rpm the timing is 21° with vacuum (21 ° without vacuum)
@ idle (750 rpm) the timing is 19° with vacuum (8° without vacuum)
@3000 rpm with vacuum is 34°
With this setting the engine is lazy above 5000 rpm and do not get above 6000 rpm


Try 2:
Added some more advance by turning the distributor counter clockwise.
The engine is getting at 6000 rpm with no problem.
The idle is a little bit more rough.

@3000 rpm the timing is 38° with or without vacumm
@idle (750 rpm) the timing is 23° with vacuum (13° without)
@ 1500 rpm the timing is 26° with or without vacuum.


The behavior of my distributor is strange.
May be it is related to the two vacuums pipes of my distributor.
One is not plugged.

Hi,
did you try to remove the cap the inner vacuum pipe is sealed with?

Maybe this makes a difference.

Regards
Norbert

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.