Talk Morgan Forums Community The Malvern Arms Missfire on bumpy roads

Hi, I wonder if anyone else has suffered this problem:
My 1999 4/4 Zetec 1850 misfires when driven on a bumpy road. The problem is particularly bad when engine is cold and accelerating away from a standstill, and the driver of a following car reported a puff of black smoke from the exhaust when the fault happens. On the assumption that it is caused by a loose wire, I have pulled and tugged at every exposed wire with the engine running to no avail. I did notice that the anti-tramp rubber bushes were worn and replaced them in case rear axle-tramp was causing load and unload of the engine, but no success.
The car runs perfectly and accelerates strongly on smooth roads.
Any ideas or similar experiences please?