Thanks Paul. We didn't have the instructions to hand and there's a note (in German) about the 1098 on their site that doesn't make sense when run through Babelfish! The span adjuster on the lever was just spinning - we had to pull the plastic cap off and use pliers to adjust - and was set to fully in (close to bar) which may have not helped either.
Unfortunately we just ran out of time to play with it but at least now we know what to look at next time to get it sorted.
I'd rather die peacefully in my sleep like my Grandfather, than screaming in terror like his passengers.- Jim Harkins