1971 Plymouth Duster with 3.7 225 Slant six Idles very rough
Along with "the usual"
Carb even though gone through may have a problem or not adjusted correctly, vacuum leak, timing bad plug or bad plug wire, bad valves or if valves adjustable, not set correctly, and on we go
BUT ONE possiblility is that somehow the Pertronix is AFU or installed wrong and you are suffereing from what is called (bad) "rotor phasing"
Google it several articles and videos on the www. This means that due to some problem in the distributor, the pickup device is not firing the spark when the rotor is actually pointing at a plug wire distributor cap contact
