Motorcycle Repair: Idle Question, yamaha xt250, fuel injector cleaner

Question
Hi. I recently purchased a 2009 Yamaha XT250 Dual Purpose Bike. Although it is a 2009 it only had 2 miles on it and was virtually brand new. I replaced the battery, Air Filter,Spark Plug and did an oil change along with the filter. My question is this, every so often when I'm riding I come to a stop and put the bike in neutral with the engine still running and the idle speed increases almost like I'm advancing the throttle approximately 10-15%. When I'm driving it it works just fine and only happens every so often. I just today lubed all the cables thinking that maybe that was the issue. The bike is still under warranty but from an out of town dealer and since I have been riding/repairing bikes for 45 years I like to try to figure it out myself. The bike currently has 450 miles on it. Thanks for your time. Raymond

P.S. It only seems to happen after it reaches operating temperature.

Answer
Raymond, Its possible that the carb is not set for you current altitude. Try this first before any carb rejetting. Put in 1/2 a bottle of Lucas Fuel Injector cleaner and fill the tank with a premium grade fuel drive it and when the tank needs refilled put the other 1/2 bottle in and repeat the fueling again. See if this helps any. The carb has a fuel mix screw but usually is covered with a brass or aluminum plug over the head of the screw so the average owner can't adjust them. It sound like its either set to lean or there is a fuel to air mix to lean by the fuel restricting a jet or passage in the circuit.