Vacuum Question M116 3.5

[350SL4spd]

My 350SL M116 is having a bad surging issue under load.

I'm in the process of getting a coil to eliminate that as the problem (let me knwo if I can borrow yours ).

In the meantime I've tested, cleaned and adjusted just about everything in the D-Jet system.

My one strang finding is this: I have a solid near-16in of vac at the vac adv on the dist w/o fail. However, I only seem to have about 5in @ the MAP. Also, if I put my thumb over the vac line off the map to the manifold, the engine starts to stall out. (Brand-new line w/ clamps MAP to Manifold).

Anyone of you D-Jet masters have any idea how I would be able to get 16in at the throttle body & only 5-6ish at the back of the mani?

Thanks.