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