Hi, I have had an update from my brother which is this:
It will start and idle fine, from a hot or cold start, however from a cold start it will only rev to about 1750rpm before misfiring, as the temp guage reaches about a quarter warmed up it revs to about 2500rpm and about 3500rpm half way up the temp guage, the guage doesn't get any higher than this during normal driving. After about half an hour it will rev to 4500rpm, then it still misfires.
I have replaced the plugs, leads, rotor arm, distributor cap, coil, CAT and 02/lambda sensor in the zorst, none of this has cured the problem.
Help - Any other ideas??