does that model have a fuel accumulator like the 450s?
they're known to go bad an impact fuel pressure.

on my recent purchase of a 76 450sl, it ran terrible (and barely)
when I got it. fuel system was all gunked up from neglect, etc.

a few bottles of Techron in the fuel system really did wonders.
I still have work to do but cleaning up the delivery system helped
a lot, and was easy.