G'day tzeggy,
My only suggestion based on my own experience would be to try a new (new) plug.
Reading your symptoms reminded me that a vintage car bloke once told me that they would often leave an air gap in the HT lead (solid wire core, I guess) without it the thing just wouldn't fire! Was completely baffled by this when I heard it and haven't been given a decent explanation as to why this should be the case. I'd love it if someone could offer a good technical explanation!
Cheers,
