After a long or fast run (talking 55mph here!), the Ghia will stutter and stall if I accelerate.  If I ease off the gas, the engine will usually idle fine, but will sometimes cut out completely.  A quick look in the engine bay shows no fuel between the pump and carb (got one of those plastic inspection things in the fuel line).

Fuel line has been replaced from the tank to the pump so I know that's not a problem.  My guess is the diaphragm in the fuel pump needs replacing, but was wondering if you folk had any other suggestions?

Yup it'll fire up and run fine for short or slow journeys, but faster and/or long journeys and it starts acting up.

My guess is that the diaphragm is on its way out.  For slow journeys it doesn't make too much difference, but on long journeys it gets adversely affected by the heat.  Just a guess really but there's no harm in replacing anyway especially if it's cheap and easy!