Needle jet is thought to operate from just over quarter throttle but actually works all the way through to full throttle (it's the fuel discharge point)
It's easier to comparmentalise the various parts in diagrams but the transitions overlap a lot
The needle and jet working together restrict flow at lower throttle positions, as throttle is opened further, the area between needle and needle jet has less effect as it's larger than area of main jet (and , just for fun, Mikuni make jets with different discharge rates with same numbers)
If you have the 'hood' type (primary choke), two stroke' emulsion tube/needle jet, you could try drilling a hole through the upright part.
Start at 1/16" then increase by 1/32" if needed up to about 1/8"
Only problem is, you don't know how far you need to go until you've gone too far
It's not even close to ideal, but, it works
I would do pilot jet and air screw, it's a very rare carburetor that has the pilot system 'switch off' above 1/4 throttle
Some Mikuni's do, but I've only seen it on CV carbs
The 'throttle valve' is the slide cutaway, do you have the 'stock' 2.5?
Where do you have fuel level set?
Try raising the float 0.5~1.0mm (so fuel shuts off earlier, lower in float bowl)
