Well - first trip to the desert with my Cousin's 2003 WR450F, and after riding 10 miles in the soft sand, his bike stopped running - just bogged down and died... There was smoke coming from the breather hose that goes to the valve cover. After a quick inspection - I immediately noticed that there was no radiator cap and that his radiator was EMPTY!!!! SO... What is the most likely thing that happed? I'm assuming something with the valves, or cams.. Any help is appreciated - my cousin is REALLY bummed, and I'm probably going to be the one that ends up fixing it! Where should I start - just check the valves?