My 1979 450 SL starts hard, miss or loads at low speed and acts the same at higher speeds. The speed is difficult to maintain at 50 or 55. it acts like it is out of time. any Ideas?

As an update I took the 450 to a MB dealers shop and they feel the problem is electrical, ie wire & etc. Expensive but I hope it solves the problem. I have had the car at two other shops with poor results , hope this works !

try putting a bottle or two of Checron Techron fuel system cleaner in the tank.
If you see an improvement, you had a clogged fuel system - injectors, lines- somewhere. If you see no improvement then you could have bigger
problems.