My brother just bought a 2006 kx 85 from a friend of his and it needed a rebuild. He and I just got done rebuilding it, which was our first time rebuilding a bike. When he did the heat cycles he noticed it would just bog down randomly, but then it would start running again just fine. It will also stall while idling sometimes. Other than it losing power sometimes it sounds fine. We think there is probably something wrong with the carburetor. Does anyone know what might be causing the problem?