Vintage Cars: 1983 380 sec mercedes benz, sec mercedes benz, mercedes benz

Question
The car strarts and runs great it runs for about twenty minutes then dies.There is no spark when I try to restart it.I replaced the coil.

Answer
sounds like you are loosing a power source, is your battery grounds good, battery good?
Coil tested and good? sized properly?
If you are loosing spark , look to electrical system , ground issue

is this a sudden symptom or gradual onset, how long does it have to sit before it starts again?