Anybody out there got a decent ESA spring / Club spares do not seem to list and mine might have been going over centre as its a bit moth eaten
Preping bike for Banbury on 19th so any help appreciated
Although your spring might be tattered, I very much doubt that that is the problem. If all the parts are correct, and done up properly, it is not possible for the cush drive to override. A very similar sensation is felt when the the sliding gear in the gearbox jumps out of mesh, usually in top but it can be in bottom. It might be worth trying to adjust the setting as described in the manual, but do make sure there is as little play in the linkages as possible.
P.