Yesterday my stock 2001 SP500 HO exhaust system heated up so much that the plastic near it melted (rear fender and side panel) and the outer layer of rust on the pipe flaked off from the manifold to the muffler. A firend riding it said it ran normally but he felt some heat on the right side, but he wouldn't know what normal power is. Now shut down until I know what caused it. Do you know?

 

check the owners manual for instructions on removing the muffler plug and blowing it out.

 

I've removed the muffler and found no obstruction. When this happened, I also thought about some obstruction, and checked that there was plenty of exhaust force coming out of the tailpipe. Seems to me that for the entire exhaust system to heat up so much, there must have been fuel burning in it. Possible?

 

It could either either be running way too rich (which causes fuel to burn inside of the exhaust system), or too lean (which makes everything run too hot). Check the following:

Mixture adjustment
Choke sticking
Intake air leak (carb base gasket?)
Exhaust obstruction (you can still feel plenty of air coming out if it's partially blocked...)
Crud in jet (clean the carb)
Timing adjusted wrong
Restricted breather (dirty air filter)

 

Thanks, Whittet. I've checked everything you listed, except the timing. Found that the valves needed adjusting. The exhaust valves were at specs (.006) but the intake valves both had zero clearance at the tappets, hence might not have been closing all the way. Could that causes such extreme exhaust heat? I suppose I should go further and remove the head and valves to check for a burned valve or valve seat, huh?

 

I went to far as to overhaul my old SP400 because of the same problem. Overhaul didn't help. Mine got so hot that the plastic in the end of the fram melted. Problem was............. exhaust system clogged. Carried the muffler down to the radiator shop and had it vatted. Problem solved.

 

I'd pull the head off, just to be sure that all is OK in there. I've never seen a burned intake valve, but if your exhaust was getting that hot, I'd be worried about the exhaust valves. I don't think that the intake valve clearance would cause this problem.

 

Thanks, I think I'll recheck muffler. It got so hot that the fender above the muffler melted like cheese on a pizza . . . that's going to be expensive to replace.