engine speed not returning to idle

This is an 82 GPz 550. The engine starts perfectly, and idles at around 1200 rpm, right where the manual says it should. However, after revving around 6000 RPM and releasing throttle, the speed stays around 3000. Way too high for idling. Seems to be worse after extended high rev, such as coming to a stop after exiting the highway.

If I hold the brake and slip the clutch so the engine bogs down to 1200 or so, the idle stays there as it should until I rev again.

This is probably a simple carburettor issue, but it's been a while since I've worked on one, so just looking for somewhere to start. I've checked the throttle return, and it closes properly, not sure where else to look. I figure if it was something like a sticking needle, it wouldn't back down after bogging the engine with the clutch.

Any ideas?

whens the last time you lubed up your throttle cable?

It could be sticking..and not letting the carb return to closed.