A symptom which comes up once in a while for no apparent reason is the tachometer bouncing up by about 2000 rpm, going back to zero, and then resuming normal operation. Another symptom is the inability to get the same dwell reading on consecutive attempts. Yet another symptom is worsening gas mileage immediately after a tune up.
These symptoms may be caused by a worn-out breaker plate. This is the assembly, comprised of two sections, onto which the points are mounted. Excessive wear will cause the points to "bounce" periodically. This can be corrected by merely replacing the breaker plate assembly, which costs about $10 and is available from anyone who sells Bosch ignitions. The replacement unit comes with points and is a drop-in installation. It is also a better design than the original unit.
Author: Michel Potheau, Tech Editor