Here is another thought, as this happened to me. This fall before storing my 650 for the season, I had the valves adjusted and the carbs cleaned. When I got it back, the bike started and idled normally, and I took it on a run. After it warmed up, the bike would not idle down during shifts, and when I stopped, the idle was just a bit higher than it was before service. I simply turned the idle down, maybe 1/2 turn, and it was back to normal.