When its pretty hot out and I'm in stop in stop and go traffic my 2000 CBR f4 starts to 'stumble' when idling. For instance, when stopped at a light and the bike engine temp gets fairly high the tach needle start to drop down to like 500rpm then back up to 1200rpm where it usually idles. Then once I start to go the engine stumbles and makes the first 2-3,000rpms jerky. But once I;m up to speed everything is fine. Any ideas??