European 1974 280SL/No Vacuum at Distributor

[alchemist599]

Hello: I am new to this forum from the US. I have a European 1974 280 R107 SL with M110 engine. I have been searching for a manual for this engine without success. This model never been exported to the US, and therefore, there is no manual was written for its injection manifold. All R107 exported to the US have a V8 engine with entirely different injection system. I found some models exported to the US with M110 engine, but they are not R107 style and all of them were equipped with a carburetor. There are manuals written for these kinds of models, such as 280C, outlining details about M110 engine, but never described the injection system equipped in the European versions. Please see the attached pic for 1974 280SL M110 engine. Is anyone knows how to get these manuals from Europe?
The problem I have is puzzling with the injection system in this car. There is no vacuum at the distributor at the idle. The distributor is connected with a vacuum hose to the venturi. The puzzling case that there is a complete vacuum at point 1 and 2 in the pic, which is good news. However, there is no vacuum at the port before the butterfly at point 3. Since the venturi which contain the butterfly is part of the whole intake manifold, and the the vacuum port labeled 3 is just behind the venturi. I cleaned the venturi and made sure the vacuum port labeled 3 is open. Is it by design? Is anyone know what is going on? The car runs well considering this situation.
Thank you.

 

[slade1]

Nothing on youtube?

 

[Bellow]

However, there is no vacuum at the port before the butterfly at point 3. Since the venturi which contain the butterfly is part of the whole intake manifold, and the the vacuum port labeled 3 is just behind the venturi. I cleaned the venturi and made sure the vacuum port labeled 3 is open. Is it by design? Is anyone know what is going on? The car runs well considering this situation.
Thank you.

Vacuum port #3 - downstream from the 'venturi' you say. Upstream or downstream of the butterfly? If upstream then there'll be no vacuum.
Don't recognise what injection system you have - or the need for a venturi. What is upstream of the throttle body (out of range in the photo)?

 

[alchemist599]

Thank you Bellow for your input. Actually, in a vacuum system there is no upstream or down stream. Vacuum (zero molecules of air) is equally distributed among the whole intake manifold including the venturi. It ends at the butterfly which is passed port 3 in the pic. Port 3 is included in the intake manifold. At idle, the whole intake starting from butterfly to point 1 should have a strong vacuum as is the case at point 1 and 2 but not 3. My question is there a valve between the venturi and the rest of the manifold by design? Knowing the fact that port 3 was cleaned and open. The vacuum hose connect the distributor to port 3 is within the intake manifold. So, why there is no vacuum at port 3? If you open the butterfly and increase the RPM, you are allowing more air to enter the intake manifold, and therefore, the vacuum should decrease and not increase.
Should the distributor has vacuum at idle? Anyone knows?