There was an unusual problem that my friend faced with his bike. After 1k or 1.5k the engine used to become harsh and the clutch would become very tight. But after he replaced the lubricant of his bike with castor oil, the changes were very much evident. When he started using castor oil even after 3 or 5 km the engine used to give great punch. Since then he has been recommending castor oil to everyone.