The bike is a 01 WR426. It has developed a hesitation at higher rpm. It always happens when I want quick excelleration and always seems to be at the same rev point. Eventually it spits and stalls. I just had a new piston and rings put in. The valves were reseated and adjusted as well. I put in a new excellerator pump diaphram...which did nothing for the problem. All the breather tubes are clear and the jets are clean. This problem started at about 20 miles with the new rebuild. Any ideas?