FMF Racing Factory Fatty Pipe for Yamaha YZ250 99-24FMF Factory Fatty Pipe Yamaha YZ250 The FMF Factory Fatty Exhaust is reminiscent of the works or custom cone pipes once used by Factory Teams when two strokes ruled the dirt. It shares many of the same characteristics with its factory works predecessors including the craftsmanship and material quality. Constructed with two thicknesses of high quality carbon steel, the lower portion is comprised of 19 gauge steel for optimum strength and durability,