Derbi GPR 50rr base settings

[Pikey748]

Hello

I have bought my son a 2010 Derbi GPR50 that doesn’t run too well and won’t start after being left for 5 minutes.
It has a Leo vince exhaust and standard airbox and filter.
It has a flat spot around 6-7000 rpm and won’t rev above 8000 rpm in 5th or 6th. Nothing much happens below 8000 rpm but I believe this is normal.
It’s currently running a 105 main jet and the slide needle is 1 notch off maximum height. I have changed the height of the needle to little effect, plug colour appears to be running slightly hot and weak, checked the reed valve which is ok. Mixture screw is 2.5 turns out.

Can anybody tell me base settings for needle height and main jet size??

Thanks
Dan