Stock muffler?... straight pipe?... long or short?...
Is this at night?...
I have a fully baffled, Harley shorty muffler... and my buddy has seen flames poppin' from it on decel,.. after a spirited run... in late evening...
It's the when, and muchness, that matters...
...(most of us just don't get that view)...
Heat plus fuel equals fire...
...