Bit of a result!
Mr Haynes says that the pilot screws should be 1 3/4 turns out + or - a 1/2 turn so, thinking it was running rich I screwed them in by 1/4 turn and tried it. Not happy.
Tried another 1/4 turn and even worse!
Backed them out again and then out a further 1/4 turn. Better. Another 1/8 turn, better again so I've gone out the extra 1/2 turn and the difference is marked.
It idles fine and now it doesn't bog down when I set off and accelerates cleanly.
Still a bit hesitant when opening up from a small throttle on the move but again much better.
I'll try it for a while and might risk another 1/8th or a quarter. Can always turn it back.
Thanks for your help.