Specify vacuum value at idle

[rutger kohler]

I am about to tune the idle rpm on my 1969 280SL.  I have downloaded the excellent instructions off this website on how to do this but I can't find an actual idle vacuum value or reading as a benchmark ("Hg) or whatever.  I do have a vacuum gauge and would like to know what value to look for.  A search in this forum, and looking at the manual still don't turn up anything substantive ( I might have had a man look as my wife would say).  One thread suggests 19" Hg but goes on to say some of the more professional manuals specify various readings for various conditions.  If we don't have a Table in the manual isn't it time some kind person put one in so grateful acolytes such as myself can use it?

[66andBlue]

Perhaps this thread below might answer your question?  Unfortunately my BBB does not have page 00-0/21, thus I cannot post it for you.
http://www.sl113.org/forums/index.php?topic=13075

[ja17]

Hello Alfred,

That information and page was part of Feb. of 1968 suppliment to the Early BBB.

[rutger kohler]

Hi Alfred,  thanks for that, it does give a range of values.  Should be enough to get me started.

thanks

Rutger Kohler

[450sl]

Tune on

Mark

[jameshoward]

I tried tuning using vacuum once, only because I hadn't tried it before and bought a gauge.

I would say that my experiences were mixed. I normally set using a strobe. I found that tuning using the gauge meant i had to make some changes. The upshot was an hour of tail chasing. It was an interesting exercise, but i pretty much ended up setting the car up by ear in the end. Vacuum settings according to the BBB are fine, but the settings were for cars that were new/ish. For one to really be able to nail tuning using vacuum readings, it may help to ensure all other factors are addressed first, like linkage, butterfly, etc. Joe's excellent tour takes care of that.

I think my engine was a bit worn to be able to make much use book values, but as i said, an interesting afternoon.

If anyone wants to buy a vacuum gauge, i know of one for sale!!