The problem: After a cold start, I drove off and made good use of the available power
A few hundred yards later, a misfire developed, plus a quantity of black exhaust smoke.
Pulled in, let it idle for half a minute or so (seemed to be on 3 cylinders) and it then returned to normal running.
A few short journeys were then completed without a problem.
Next cold start, dropped on to 3 cylinders within a couple of seconds, gave it some revs and it cleared.
A couple of days later, started up, seemed normal, took revs up to around 4,000 and took my foot off the accelerator. Engine slowed and cut out. Tried to restart and was turning over very unevenly (just like a petrol engine with a plug removed or burned out valve) then flattened the battery (it's the original from when the car was new!).
Returned to car 10 minutes later, battery had recovered and the engine started straight away on all 4 cylinders.
So it seems to me that a valve is sticking open randomly..........can anybody tell me why??
(Oddly enough, my old Rover 214 used to do this from time to time, but I was able to live with it as the car had done a lot of miles, owed me nothing and I had heard that the K-series was prone to sticky valves anyway)