Thanks for that I read somewhere the rev limiter is set at 6800 I have no intention of revving my bike that high anyway, I have reset my float height, so hopefully that will sort my problem.
My brain is rather addled these days, but I think you'll find that's the rev limit on the accessory Pro Race kit ignition module. I'm sure someone with more active brain cells than I will be along shortly to confirm. I recently bought a new Dyna 2000 programmable ignition box cheap as chips for one of my bikes. One of those might be a useful alternative to the standard ignition box if that's what's fitted. It has a few settings to tweak, like ignition advance curves and rev limiters, choice of dual or single fire mode etc.....
As others have said, by far the biggest bang for the buck upgrade to any European tube frame bike is full USA gearing but it sounds like your bike likely has that already.