If you haven't replace the Distrubtor cap, rotor arm, plug caps (only use NGK or well known make), plug leads then change them all, the Distrubtor Doctor (google search will find him) is a good supplier of rotor arms the Lucas replacement ones are rubbish short between rivit and retaining clip, Auto Electrical Supplies are usefull and Lucas cheap coils etc, I dought if it is the coil unless its very old easy to swop over from 61?
( my misfires have been plug caps /dist caps/ rotor arms , I alway keep a spare set of everything now makes hunting the missfire easier!!)
Low battery volts will cause a missfire if you have electronic ignition
Brian
Edited by - Brian Soper on 22 May 2012 13:11:48