I have a 93 Yamaha 650. I think it's LX not sure. It looks exactly like the wr500 except the engine. Well I let a friend ride it and he flipped it over several times. Still ran but got water in engine and sat for a month. Tore engine apart got all water out and everything looks fine but it makes this kinda like thumping or knocking noise now. Can't figure out what it is. Does anyone have any ideas?