Odd adjusting screw on throttle body. Ideas?

[Worldflier]

Good day,
While chasing my warm starting issue, I removed the throttle body (throttle plate assembly?) from the intake manifold and noticed a tiny set screw near the back of the assembly.

Does anyone know for what this is used? It connects to a vacuum port in the body, but spraying cleaner into the hole didn’t reveal where it leads.

Btw, this car is a 1967 230sl with the M127 engine.

Thanks for your ideas!
Dre

[Worldflier]

One more picture.

[Pawel66]

Is it not a vacuum port? For certain tests.

[Peter]

Just what I thought.
See Hayne manual.

Peter

[Tyler S]

That grub screw is very small, non magnetic, and blends into speckled epoxy flooring. Never did find it.

[wwheeler]

I have seen that test before and never knew what grub screw they were talking about. Interesting. Anybody ever done that vacuum test? Seems like the split linkage test would have about the same effectiveness and a whole lot easier.

[Tyler S]

Wallace,
I have done that test before and all it really gets you is a visual representation of the vacuum level at closed throttle. It isn’t much different than the split linkage test.
BTW there is one part of that procedure I do during a split linkage test. I disconnect and apply my own vacuum to the distributor with a hand pump as it can skew your results. On an 051 distributer, The timing advances when you crack the throttle via the vacuum retard setup. Even if the engine is lean it can raise the RPM significantly as advancing timing will allow for a leaner mixture.

[wwheeler]

Good point and I will try that! Thanks for the tip. Maybe add to the Split linkage tour?

[Tyler S]

I edited above to include that I use a hand pump to supply my own vacuum to the distributor. Not sure how I forgot that part.

[col320ce]

I made a plastic connector to measure the vacuum where the screw is... Worked well. Then broke it and tried to make another out of brass but failed.