250 SL Manifold Vacuum Spec

[Atazman]

Gents.....

Can someone provide a specification (if there is one) .......or a typical intake manifold vacuum value...... for a well-tuned 250 SL engine at idle speed of 750-800 rpm?

Right now I'm measuring a steady 16 in. of Hg vacuum.  I would think it should be higher but that's what I get when my idle speed is under 800 rpm.  I'm thinking my injection system is a little too rich at idle, but I have not been able to make that adjustment on the pump.  I'll have to take off the big hex nut to see what is happening inside the injection pump.  No CO meter either.

Thanks.....

[Benz Dr.]

Manifold vacuum is dependant on many different inputs such as condition of engine, timing anf even altitude.
16 inches is a bit low. What do you get at 1,200 RPM? The actual reading is important but what the needle is doping is just as important. If it's steady that's a good thing. What happens if you change the timing?

[Atazman]

Thanks Benz Dr...........

Appreciate your feedback.  I don't have the answer to your question about the vacuum at 1200 rpm.  However, I have made progress on getting my idle "right".  Thanks to this forum, I found out that my FI pump has its own sump.  I finally found the dipstick and when I opened it, oil ran out.  Lots of oil ran out.  Thankfully, the oil appeared to be good oil, and not diluted with fuel. 

Years ago (prior to me knowing about this forum) I knew nothing about the FI pump, and since it had a red oil cap I thought it needed oil.  Unfortunately, I used the plug in the side of the housing as a means of determining the correct oil level.  I filled it until oil ran out the plug.  So I'm guilty of creating my own idle problem.

Today, I got the right level on the dipstick and started the engine up.  Now..... the idle is nothing short of "perfect".  I don't know what the vacuum is because on my last attempt at vacuum measurement, I found the threads to the intake manifold nearly wiped out.  I don't want to mess with this plug again until I can retap it.  I just opened the air adjustment and the idle speed is now very stable at 800 rpm.  I'm running it to the high end of the spec because when my air conditioner compressor kickes on it will bog the engine down a bit.

I'm a happy camper now.......thanks to the wealth of information provided by this forum.

[glenn]

Clymer's 'Mercedes-Benz Tune up . Maintenance  Gas and Diesel 1958-1974'  Publication A180.  It has 15 different vacuum gauge readings/conditions on page 10.  Page 9 says 18-22 inches.  Page 10 shows 15.  Subtract 1 inch for every 1000 ft. of elevation.   Go figure??   Every/most auto books has/have a 'vacuum gauge' section.