vfr400 runs perfect up to 10000 rpm then stutters as if starved of fuel....
Bike is a uk version

Have similar issues, my question is................is it in all gears or just in 6th?

When did problem start.

Have you got the little rubber flappy thing (Between airbox and carbs) fitted properly? If not you will get disturbed airflow that makes your bike run like crap....ask me how I know.

bike has run like this since purchase

Little rubber flappy thing is fitted...
What is the correct route it should take?

May be you need to start with a check of the fuel system ie jet sizes, fuel flow, etc.

is it standard? Air filter, snorkel on the airbox in place etc?
NO point trying to fart about with them - get it standard and it will be wonderful... it's never going to have millions of HP so it needs to work to it's advantages