My bikes a 91 gpx 250. Stopped top of mountin after 30mins hard riding. Let bike sit 5 mins off. When i turned it on bike reved to 5ooo revs thinking maybe choke stuck got it in the off position stayed fideled for 45min. Before riding back it just would notgo below 5000 when got and stopped after only bout 10mins riding the bikes revs dropped to the normal 1000. And since no problem. Any ideas? Float in carburettor problem? Just a bit hot??