I'd say more than likely that the exhaust is probably stuffed with waste two stroke oil. Only cure is to unblock the exhaust by taking it off & putting something like caustic soda down it. This will soak up the oil & get blown out through the exhaust once it's back on the bike with the engine running.
If you don't fancy doing it yourself, I'm sure your local bike shop will only charge a small fee for this job.
Steo
November 2009