I have bought a 2year old Lifan LF200GY-2 trail bike with 347miles on the clock. The bike ticks over lovely but if i try to ride it it cuts out and if you do give it some revs it coughs and splutters and makes a sound like a car or bike with no air filter in so you hear this BAAAWWWW but at road junctions it cuts out yet it ticks over ok even after you rev it up. I have twice stripped carb down and cleaned all jets with carb cleaner and they look clean reassemble but still the same.
The plug is clean and gapped, petrol tank tap bowl is clean and fuel flows freely from it  and i have a brand new battery. The needle settings is set on the middle setting and a friend set the mixture up who build motocross bikes but haven't seen him so i thought id ask the lifan forum.
Do you think i should raise the needle and readjust air mixture or could it be a jet problem as I'm completely stumped. help