Momentarily losing power

[Farmingstock]

The bike is an unrestricted Honda NSR 125 with carbon reeds and full arrow exhaust.

The problem is the bike starts fine and goes ok ish, although when riding mid range 4-8000 the bike will feel like it's lost all power (if you Rev it it sounds like it's just sucking air in but not running) until it gets to 3-4000 revs then will Rev up again until it does it again, if you keep it low revs or high revs it won't do it just the mid range. Scary mid corner or cruising and you think it's going to cut out.

So the issue is more mid range, although the engine will stay at 3000 revs then slowly lower to tickover if that is related.

Don't know how else to describe the issue but hopefully you understand what I mean