Mercedes Benz repair: 1973 450se stalling, ballast resistor, grey market

Question
i have a 450se 1973. lately it randomly starts to conk out usually after 20-25 mins driving. it takes quite a few turns to restart and black smoke comes out.  any insight or articles to help understand this. any mechanics in ny metropolitan area  

Answer
Questions and data needed:

Miles on the car?

Geographic location = nearest major city?

Is this a California car or Grey market import?

Please search the exhaust system for any sign of a catalytic converter between engine and muffler?

Have you ever replaced the ignition coil?


From your description, the odds are 90% in favor of a thermal ignition failure.

* Corroded wiring or terminals?
* Failing Ballast Resistor?
* Failing Ignition Coil?
* Failing Ignition Control Unit?
* Failing Ignition Points?
* Failing Trigger Points?


Depending upon condition, the odds are only 10% for these units causing your issue.

* Failing Ignition Wire Set?
* Failing Distributor Cap?
* Failing Distributor Rotor



Diagnosis changes if there is a catalytic converter between engine and muffler, it could be plugged.