I bought a 2001 xr 400 wtih a White Bros exhaust and was re-jetted to 58/162. The bike was hard to start and would backfire on decel, old gas. Decided to clean carb, took it off the bike and cleaned it. The bike now starts on the first kick and idels great. However, I have a new problem, at about half throttle to top end the engine does nothing but sputter, sputter, sputter, no power. Help please!!!!: Any ideas/suggestions would be greatly appreciated. Thanks !!!!