Stutter when accelerating hard 5000-8000 rpm range

[PieEater]

Very true mate, but it would do it in every gear, this chaps problem is only happening in second.

I'm not saying it is the issue mate, I'm just mentioning that it would be worth checking, and it still is. There could be any number of reasons why a partial obstruction to airflow might be more noticeable or only evident in lower gears. You can't necessarily pin the throttle back in all gears, second is probably the one where you can, first will have you flipped off the bike, third will have you doing insta-ban speeds and potentially having to be more cautious of traffic and turns. The obstruction if it's on a wire / string / elastic like mine could be pulled through into the airbox whilst in second gear clearing the obstruction and then once the bike and suction stops it could be pulled back out again setting it up for the same thing to happen next time. You just don't know, so it's definitely worth checking, even if it's unlikely.