Putting a old 280C with 88669 miles on a m110 engine back on the road and its barely runs sometimes. will not idle.

Backfiring through the carb. and have checked timing. new point, firing order,spark plug wires, checked for vacuum leaks,
all OK.
What next.
Also what is the device on the front of the engine left side. with hoses going to manifold vacuum and power brake booster. and can i bypass it and go straight to the brake booster. Almost all the photos i find of w114s with this engine do not have this device and the hole is plated over.
This is a Calif car but no longer needs smogged

 

The problem you have sounds like a classic vacuum leak. I would first plug off for testing only the manifold vacuum connection. This would plug off all the vacuum operated devices on the car. I have an 80 so I have fuel injection. Take a look at the plugs, what is going on with them? What color are they and are there deposits on them that may give a hint. Should the car idle with this vacuum plugged off then it is a matter of finding the vaccuum leak. Plug it back in and then where it branches off to door locks, booster, climate control and others plug them off one by one.