maybe exhaust is still blocked?  Try without silencer...put the exhaust onto a charcoal fire?  Perhaps the little turbo spark arrestor thing that spins the ash is still plugged, which is feasible since its very small to begin with?

I think removing the end out of those doesn't get to the spark arresting bit deeper in. Latter DT's the complete tail muffler comes out of the main chamber. Burning out you realy need to see some action so buring carbon is getting out. Just don't burn the village down.