I have a '99 WR400 that has just started running very lean and hot... in fact the exhaust header turns orange it is so hot and it melted all my plastic over the muffler. It will idle, but it bogs down and stalls when you give it gas. I have had it in the shop a few times and they say that everything associated with the fuel delivery system and carburation is OK, but it still won't run. Now they want to tear into the engine to try to figure out what the problem is. Any ideas before I drop a few more bennys on this or should I just got my losses and upgrade to a new 450?