My 01 AC 400 has developed a fast idle when in neutral. It wasn't there before and I haven't changed anything on the carb. What could be causing this?

 

Throttle cable adjust? Small piece of dirt in the carb somewhere? I doubt the idle adj screw got moved.

 

I had the same problem with my 400, there's a thumbwheel at the back of the carb, better accesed from the right side of the bike. Looks like a rubber tube, and has a plastic **** on the end. I turned mine down, works great now.