I'm with Jay on this one. You've got a fire side problem, not a fuel side
one, I think. Ignition relay is a real good bet. As a backup, I'd have a
look at your condensor unit (if you have points installed) or the elec
ignition unit (if not). I had a Ford truck do this to me when it's little
Motorcraft brain decided to go into a permanent coma. Took several weeks to
completely die, though, with intermittent faults much like what you're
75 MGB 'Rags'
Wouldn't have a Lucas ignition unit if you gave it to me