My buddy has a '99 XR650L. It ran great before it sat for a couple months. Now, the bike sputters and cuts out slightly at upper rpms. The air filter was cleaned and re-oiled, new gas and the carb was cleaned. The bike still sputters at upper rpms. Now, he bought a new battery before this problem popped up. He bought the cheapest WalMart battery that fit the bike. Could the cheap battery be the cause of the upper rpm sputtering and cutting out slightly? It didn't do this before the cheap battery was put in. Thanks in advance for any help on this matter.