For anyone else looking for info on this part of the 750EX, I've managed to find a German video which answers my question
The video link is here
I'll have a look at my mower tomorrow and it should be clear. I think one problem is that I may need to loosen the carb to allow the hook to go in...
I was just cleaning the carb on a B&S 100802-0121-H8 which I believe is a 750EX ReadyStart Victa Mustang mower engine, but the sticker has come off before I bought this.
One of the linkages (governor?) disconnected and I can't see where to attach it back. It's probably not easy to explain, but...