Thanks for the advice ... the fuel tank cap vent sounds like a
distinct possibility, so I'll check that out. I should possibly
explain what is happening a bit more accurately. The motor's rev level
becomes unsteady and becomes a mixture of slowing and or misfiring,
and then cuts out. Its not like it happens all of a sudden, and I can
tell when it is going to cut out, but I don't seem to be able to stop
it happening ... seems to happen at the worst possible times too...