Fix those cables and ride it for some miles. It could be dirt in carb if it sat for longer time. My RK has werid idling after long winer but it gets better ride after ride.

 

I'm pretty sure it is the cables need adjustment or lube. The PO rebuilt the carb last summer and rode it a few times a month since then. He also drained the carb bowl after each ride if it was going to sit for a while.

 

I had the same issue with the throttle not snapping back. When I put new grips on it, I lubed the cables and readjusted them and it was fine. 99% sure the cable adjustment was the problem.