Help me before I loose the will to live!!

Right this is a subject I'm about 10 years late too but I have spent 2 years trying to solve this!

I've got a 2009 EXC450 and the issue I'm having is an off idle bog and a hanging idle. It's not a terrible problem and most people would probably just ignore it but I'm a perfectionist and won't rest until I've solved it.

Things I've done:

Midbody gasket replaced 

JD jetting kit

New Throttle slide o ring

Accelerator pump squirt timed and duration set along with o ring mod

Throttle slide track smooth and the slide doesn't stick when testing statically.

Things I've noticed is that off idle it runs like a dream but when snapping the throttle it bogs out, also when playing with the idle speed I can eliminate the bog but the idle then hangs until I blip the throttle again. This made me go up to a 45 pilot from a 42 as supplied in the JD Jetting kit but no difference.

Also when playing with the fuel screw I have to wind it virtually all the way in before it makes a difference and then it increases the idle as if its lean but otherwise I can wind it out past 2.5 turns with no difference. I've checked for air leaks and there aren't any plus it's just had new piston, timing chain and all valves de coked.

I've read pretty much every forum post and watched hundreds of YouTube videos and at this point I'm ready to give up and spend £400 getting it send to Tokyo mods in the US. Spoke to my local KTM dealer and they were no help just said it is what it is but last 4t carb bike was a 2008 CRF450 and I don't remember having any issues with fuelling.

Please can one of you Internet geniuses help??