Simon, You may want to look at the screen in the gas tank. I had a similar problem where the car would run for a little while cut off sit for a 2 or 3 min and start back up run and repeat. My first thought was vapor lock. After tracing the fuel system, I found trash in the tank. AS i drove the car the fuel pump would pick up trash off the bottom of the tank, starve the carb,car shut off,trash fell to bottom of tank, crank the car, start over. May be something to look at.