After a week of tinkering I still have got no further, I have taken a short (probably the least interesting video in the world) so that someone with a bit more knowledge might be able to help identify the struggling sound!
I didn't renew the gaskets when i put the carbs back on as the ones that were on there looked ok? Would an air leak there be sufficient to explain the struggle?
I have also been adjusting the brass screws, it does make a small amount of difference the further out they are, but even when they are 4 or 5 turns out (and about to fall out!) the open throttle still isn't there? It does make it very rough at idle though!
As per the timing, the linkage is pushing it right round until it hits a stopper, i could move this stopper as it is only held on by a bolt but there is no indication of where max is? just lots of lines!?