shutty123

Hey guys ? been out on my mate on my gas gas and his sherco today, after about 10 mins of riding I've noticed there was a lot of blue smoke behind him, at thought it was probably just a little rich but after another 2 mins he said she could smell burning, after checking over the bike the rear mudguard and bottom of the tank have melted on the back box and mid section, even after cutting the bike there was still smoke leaving the exhaust for at least 5 mins...I have honestly never seen anything so hot,..the back box was that hot it's melted the plastic exhaust guard straight off, So anyone know own what can cause this? The only thing I have changed is a s3 titanium front pipe, can't see it making much difference? I didn't run it again to check to see if the fan was working as I didn't dare run it again, Has anyone ever come across this? Thanks guys...