I just experienced they same issue. I put the bike away over the winter and treated the gas with stabil, as I always have.
I started the bike last week and it didn't want to die without the choke. Common issue - I cleaned out the carb (no thanks to Stabil) and put things back together.
Bam, first kick and she was purring. I took off the choke and the bike went from idle to high revs. I adjusted the idle screw and it eventually came down, but wanted to die. I adjusted the idle screw to bring the idle up a bit. It was idling well, then without warning began to rev like crazy!
Also, if it is idling and you hit the throttle, it will stay up on revs for a very long time.
Sound like an air leak somewhere?
Thanks!