I think maybe your friend used old, cruddy gas. In my experience, Honda's carb jets can clog easily from contaminated gas. During my last clogged jet problem, I would take the carb completely apart and soak it in carb cleaner. The motor would run like a top for a week and then go south again (same symptoms as yours). I'd clean it again and get another week. It was recommended that the carb be cleaned in a ultrasonic cleaner and that was the only way to really clear a clog. I didn't have an ultrasonic cleaner, so I ended up buying a new carb body and that resolved the problem.