Graham this was exactly the problem.....
I swapped the front & rear cylinders as a few people have sugested.
i now have .625 rear & .700 front....works well although not driven on road as its still being rebuilt ,but the pedal has only a small amount of travel.

I did have to lengthen the pushrod for the front cylinder which improved it further still.

Can you explain why lenthening the pushrod to the front improved things..

cheers Graham