Thanks clogs. I confess I hadn't thought of using an inner tube. The valve might make it a bit lumpy but it is an idea worth investigating.
Ian, it seems that like me you have the "two speed" version with a gearbox. There should be a noticeable difference in blade speed so it might be that something has come adrift. If you do have to stip it down it isn't difficult. There's a nifty little selector mechanism that might need sorting out.
Watch out for the detent ball and spring. They will seek out a hiding place in the workshop if you aren't careful. Guess how I know! There's a grub screw to undo that allows you to extract the spring first.
You say the leaver moves and there's a noticeable click. There should be two clicks, one at each end of the travel. The leaver moves through a full 180 degrees. Are you getting full travel and both clicks? I'm sure it can be sorted.
Good luck and please post your results.
Edited By Rex Hanman on 05/05/2017 09:05:47