[RSW]

It was the same as prev described re: when cold it was better.
THe local Porsche dealer said it could be an air leak that let the car run OK when it was cold as the choke gave a rich mixture which compensated for the ammount of air then it lean'ed off as it got warm and started to play-up.

I've got all the pipes off - can't find any problems with any of them so if I get time tonight i'll re-fit and check something else.