Hello to all! Bought my son a slightly used bike. When got it would start, idle great but would stall after giving more Than 1/4 throttle. Choke would help alittle. Reads the posts, pulled and cleaned tank, carb and fuel valve. Replaced main fuel hose, filter, pilot jet, top cap of main jet. Cleaned carb thoroughly and adjusted fuel air screw under small cap to 2 1/2 turns out. Bike does the same exact thing. Fuel is new! Help!