My son's '05 KX125 is a screaming demon... or at least it was until last week. We just had a new top end done (piston and ring) and also replaced the entire clutch assembly (basket and all). Last weekend on the fresh top end and clutch system he did 2 or 3 practice motos and 3 full race motos. Halfway through the 4th race moto, in the middle of a jump (in the air) the bike starting spitting and sputtering. He tried opening it up but it just ran boggy and ran like the choke was on. We have been trying to diagnose the problem and in the last week have tried cleaning the carburetor, checked and cleaned all the jets, checked the air screw and needle position, tried multiple spark plugs, checked the cap and wire, changed the CDI box, changed the stator, changed the silencer, drained and replaced the fuel, checked the choke, and double checked the piston and ring for damage. When bike is sitting on the stand and you open her up it sounds like it's hitting a rev limiter (even though there isn't one). Bike will clear out when the wheels are on the ground and you open it up but as soon as the back wheel leaves the ground it's back to sputtering. Any ideas are welcome... we have tried everything we can think of. We only have six more races and we are in the #1 spot in the MI State Championship right now... we will try ANYTHING!! Thanks.