I recently bought a 2004 yz450f and the bike heats up pretty fast. I started up in my driveway and I rode it down the street with my shorts and the heat was strong enough that I could feel it pounding on my legs. I don't know if this is normal but I'm back into having 4 strokes. I had a cr250 2 stroke and it wouldn't give off this much heat. I had a YFZ450 quad that also heated up quickly and did the same thing.. I'm pretty sure that was normal but I don't know if it's a Yamaha thing or a 4 stroke.. Just trying to clarify to see if everything is running fine.