We have a 1997 SX250 that was once raced by NZ's Shane King. With the throttle closed, the motor suddenly revs up as if someone was blipping the throttle. This also occurs while riding it! We have stripped it down expecting to find a blown base gasket or crankshaft seal. The seals are all perfect, we have replaced the gaskets, piston rings etc. The ehaust is sealed in the barrel, the reeds are fine, the intake manifold is good, we have stripped and checked the carb, and even replaced it with another. The bike continues to start and rev up and down by itself with the throttle closed, and cable slack. Any suggestions????