Boyesen PRO-126 Pro Series Carbon Fiber Reed Fits: Yamaha YZ250 1999-2000 Pro series reeds use a carbon fiber top reed coupled with a durable fiberglass/epoxy bottom reed for quicker acceleration The top Carbon reed is lightweight and resilient for crisp throttle response at partial throttle or low RPMs; The stiffer, bottom reed is ported to provide maximum flow and horsepower at higher RPMs Offers a quick and accurate reaction to piston speed for smooth dependable throttle response Increases performance without sacrificing the life of the reeds