Kawasaki Forums - klr 250 problem knocking/grinding

Hi there, ive got quite a serious problem with my bike and was wondering if anybody could help, ill start from the top... Brought the bike with 17k on the clock, then rode it about 130 miles to kent, when i got there it wouldnt start so i checked the valves, ajusted them and then it ran perfectly for a couple of weeks untill today, i was riding about 65mph and i started getting a really nasty knocking sound coming from the engine, it seemed a bit like a pattern, i guessed my valves were a bit loose as ive never heard anything like it, so i rode on and parked my bike up. Jumped on my bike after a good 9 hours of standing, kicked it and it started first time but still with the same knocking sound, i noticed that it was worse when idleing, but maybe that was* because of the other engine noises, so i rode about 10 miles at around 25mph then went to 50mph after a couple of mins my bike completely lost power and there was a nasty grinding noise coming from the engine i couldnt go over 40 mph or over 4k revs because it would just die all together, i got to my house, let go of the revs and it cut out straight away, im hoping this mite be a top end problem as i have tools and a little bit of experiance of working on it, need to get this problem sorted asap! So aby help is really aprichiated!