'83 380 SL poor running when warmed-up

[380sl sedona az]

Hi folks; here is the problem: car will run perfectly fine until temp reaches 80c, at which point it suddenly loses vacuum (as indicated by economy gauge) runs rich (indicated by black vapor - not a great deal) and generally runs crappy, with notable power loss. It does not stall and idle remains fine. Once car has cooled for maybe 30 minutes all is well again, until its not once temp rises.

It used to do this very sporadically (like maybe once every two months) but now happens every time I drive it.

Nothing looks amiss in the engine bay upon visual inspection, vacuum lines appear to be fine, no loose wires, etc..

I've been researching this until my eyes bug out. One thing I keep seeing mentioned is the warm-up regulator or WUR. Can anyone offer advice? Thanks

[INSIDIOUS]

The A/F ratio can be tweaked by that adjustment port through the top of the air cleaner housing.