"Is it that "CO adjustment" screw in the fuel distributor, and if so, what size and kind of tool (t-handle allen hex) fits?"

Yes, that is the "CO adjustment". Use a long handle 3mm hex wrench. It's a tight area for a T-handle. For extra leverage, if needed, I use a short piece of metal tubing slipped over the short leg.

Before using the 3mm wrench, get down in there with something that will pick the crud out of the 3mm set screw as much as possible. It may be stuck, and you need to get the wrench way in for a good bite.

Adjust in small increments CCW (Left) for Lean, Right for Rich, with engine warm but off, then restart. As little as 1/4 turn can make a big change sometimes. I usually back off till it stumbles, then go rich till it runs smooth. (But it's been a long time now.)

I don't know about bleeding off pressure at the CPR/WUR. Interesting theory, if you just want to go richer. Let us know how it works.


--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Now gone)
'83 Turbo 245
'73 142 (98K)
'71 144 (track modified--and still here)
New 144 from '67 to '78
Used '62 122 from '63 to '67