Hi Bax,
Thanks for your response. I know the OS book says don't disassemble the pump but having done so I can only say that whilst it contains a few small parts it seem s very straight forward. Because there is no going back I have persisted and now have the motor running again. By the way it won't run unless the pump is working! (I have certainly proved that point)

I'm not certain that I have it 100% correct but I will be testing it further over the next few days. Incidentally the Japanese instructions which were supplied when I bought the engine in Japan does show the pump assembly as a separate item.

Thanks again for your interest and your response.

Macchiaus