Those Wings have 4 CV carburetors and the vacuum-actuated slides are machine fitted into the carb bodies. No rubber diaphragm or anything. These have to be spotless and true to work properly. The carbs are also finicky and have very small passages and even though they are in plain sight they are no picnic to R/R. A popular mod was to fit a small 4 bbl auto carb and I believe some factory even made a manifold to do this.
Also the timing belts should be replaced (30 years old and sitting under tension around pulleys for a while) before running the bike. This is a job best done by a pro. Not expensive or too difficult but catastrophic if bungled.
Brake fluid, coolant, lubes and fork oil should all be freshened.
I had a friend that stripped a GW like this for a group Colorado road trip. He was able to keep up with everybody and run away from some. Of course he was a good rider but the bike performed well and looked good this way.

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1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".