Check the fuel filters, one in the engine bay, and the one in the electric pump in the rear.

I bet your problem is there in the rear pump filter, esp. since it seemed to run better for a time after the fuel lines were cleaned.

Thanks for the suggestion Peter. I don't have an electronic fuel pump only the standard mechanical one. I did replace the fuel filter early on in the piece and out of interst cracked open the old on, it was very dirty but the problem continued after the new one was installed. I drained the tank and checked the fuel and it seemed quite clean.

Anyway, the carbie transplant was completed today and the car seems to be running a lot better, although it sounds a bit rough because the muffler has come loose. There's always something isn't there?