i know this thread has died of natural causes, but thought i would give an update.
while the FSM says vacuum advance is only about 10 degrees, i have no idea if that is also the case for the mopar electronic distributor i have in there, .
so, don't know if this was my issue yet, but this is certainly one thing out of the picture!
(1) Mick this thread died of unnatural causes (2) the # stamped on the arm actually in there will tell you the circumferential "arc" distance the rotor will swing back & forth in (in degrees but easy math will let you convert it to distance if you are into that). (3) Also you might check/correct the radial distance between the rotor tip and the cap terminal (ideal is .015-.020 ish). any more than this forces the spark to jump a greater distance/more area creating more carbon tracking from the excessive flame and it also increases the required voltage to jump that excessive gap.
