About a week ago my 2.25 petrol abruptly started running rough. It started easily, idled smoothly, and was smooth at high rpm - above 2000. After checking the points gap, (points, condenser and plugs were replaced last service, only a few hundred kilometres ago) I decided it must be the Zenith, so pulled it to bits - no problems, no better. A rough crank test showed even compression (thought it could be valve seats, since I do not have hardened valve seats) although it is not long since it had a decoke, so I would have been surprised, although could be a tappet loose. Finally, yesterday, tried pulling off plug leads while at a fast idle - number three made no difference and what is more, there was no spark when the lead was close to the plug. Examination showed the lead had a resistance above 20 Mohm and no core for an inch from the terminal each end. Replaced the lead with one from an old engine, and will have to get a new set of leads next time I am in town.

This is the first time in nearly sixty years of playing round with cars I have had this problem - leaking leads, yes, but not open circuit!