I have had the same problem with my 79 , and I am still trying to figure out what could be causing it to quit. I have done a complete tune up, had the carb off three times, and am now convinced it is an electrical problem because it quits so suddenly. That is it does not seem to act like it is running out of fuel (blocked jet). The points look good, so now I am looking at other things. Any ideas would be appreciated. Thanks