set timing

[raueda1]

SOLVED!!

I managed to get the vacuum unit off the distributor.   The problem became quite clear:  somebody had buggered around with it in the past and bent to arm from the diaphragm to the plate in the distributor itself.  The bend didn't bind the arm going outwards toward the diaphragm, allowing the vac advance to work.  However, the bend did not allow the arm to move inwards towards the distributor body, so the retard was effectively prevented.  Putting a vacuum on the respective ports moves the arm as intended and the diaphragm holds a good vacuum, no leaks.  Very nice!!  Whoever messed it up also cross-threaded the little screws holding the vacuum unit on!!  .  !@#@!!@!#@!!! I'm going to try to retap the teeny press-fit bolts on the distributor wall and use new screws. 

It's become clear to me that these cars are often able to run surprisingly well even when stuff isn't right and normal civilians (unlike us here) might not even notice.  This goes back to the repeated theme that you need to check everything imaginable to make sure it's right.

I was going to put it all back together and test it before posting.  But this discovery excited me so much that I couldn't wait --  it's pretty clear that the problem was identified and will be fixed when I get it all back together.  Assuming I can get the distributor back together and installed right. 

Getting closer every day . . . .

[rumb]

No doubt we have all seen very strange things that previous owners have done that make absolutely no sense. 

Methodical investigation will get you there eventually. Glad you are on the right track.

[raueda1]

No doubt we have all seen very strange things that previous owners have done that make absolutely no sense. 

Methodical investigation will get you there eventually. Glad you are on the right track.

Yes, yes and yes.  The solution is now confirmed. The advance advances, the retard retards and the AC switch for does what it's supposed to - the idle holds (or very close) when AC is turned on.

So it's all good.  Or maybe more like 95% good -- not perfect but vastly improved.  The newly working vac retard only retards by about 4° at idle.  However, at 3000rpm/no vac the advance is about 30° and 40° with vac advance hooked up.  That gives 10° at idle without the retard.  With the retard this is just reduced to about 6°, not quite 0° TDC +/-3° as per the specs, but close enough (unless anybody can convince me otherwise).  Since the entire purpose of the retard function seems to be to manage idle speed with AC, and that works, I'm not very troubled.  I hereby declare victory.  When the CO analyzer and tach/dwell meter arrives I'll revisit and retweak (I was judging 3000rpm by ear). 
Special thanks to Rumb for this.  I'm standing on the shoulders of giants!

[Guru]

A great thread. Does anyone have a PDF for the procedure and values for a Euro '75 450 SEL? As far as I can tell this is the earliest and simplest setup (ie a single switchover valve).