What causes the idle to fluctuate?

Bike is a 2006 KX250F that we just bought. Jetting is box stock, so I know I need to start playing with it. Bike has ran fine until recently when our weather has gotten warmer. I need to check the pilot, that's the first step right? I know everyone says to use the 42 pilot in that bike.

Problem we are having right now and before I start playing around and make it worse I want to know what would cause it so I go in the right direction. When you rev the throttle or ride and come to a stop the idle will be high. After a little bit the idle will drop back to normal. Would the pilot circuit cause that? Lately is has dropped to the point the motor dies, cost my son a race the other night when he couldn't restart.

Is the first step on jetting to do Eddie's sticky on how to check your pilot size based on the fuel screw setting? That was my plan, but first what would cause the idle issue or does that solve that problem?

Sorry for the rookie questions, I have always had 2 strokes, so I have to learn what to do on the four strokes.

yes,thats the first step.that will tell what direction to go.

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