1985 BMW 735 wont start

i bought the car about 2 months ago about a week after driving the car i was on my way home and the rpms dropped while i was driving about 50 mph and the car missfired and stalled i have replaced the plugs,wires,cap,and rotor and the car starts sometimes but 99% of the time it starts and dies after about 5 seconds the one day i got it to run for about 30 mins in the driveway (i was stuck in the snow) once the car reached operating temp it stalled and died so i pulled the plugs and they were black like the car was runnin really rich i dont know what else to do can someone please help