Hello: I am posting a puzzling issue on 1974 280SL, R107, European version with M110 engine. I know this post is not within the scope of Pagoda's group, however, I could not find any literature covers this engine. I though that someone at the pagoda's group might be familiar with this engine.
The issue is that no vacuum at the distributor at idle. If you see pic, I marked 3 points at the intake manifold. I have full vacuum at points 1 & 2 but not at point 3 which is the venturi area. There is a rubber hose connect point 3 to the distributor. I cleaned the venturi and made sure that port 3 is fully open. The puzzle is why there is vacuum at points 1 & 2 but not 3, knowing the fact that port 3 is a part of the intake manifold and it should have vacuum when the butterfly if fully closed. The car runs and idle well even with no vacuum at idle.
