M-Spec YamahaYZ144 Big Bore Kit

M-Spec Complete Big Bore Kit (Part #YM125-MT-BBK12) $489.95

The 2-Stroke Revolution is real and our YZ144 M-Spec Big Bore kits truly make your 2-Stroke equal to or better than modern 4-Strokes.

The 1999 – 2018 Yamaha YZ125 134cc / 144cc kits are our most popular M-Spec Big Bore Kits! We strip your stock cylinder, weld the ports for perfect port timing, then bore the cylinder from 57.5mm to 56mm (134cc) or 58mm (144cc). The cylinder is then hand ported for your riding style. The cylinder head and deck surface is also modified for better sealing and optimum squish. The bore is then plated with our proprietary Nickel Silicon Carbide plating process. The power valve is modified and serviced and the entire assembly is shipped out with a custom forged piston and complete gasket set.

Woods, Race, MX or Off-Road, our M-Spec 134cc and 144cc Kit will make your YZ Fly!

Applicable Models

1999-2018 Yamaha YZ125

R1 Chamber

Yamaha YZ125 Yamaha YZ134 Yamaha YZ144 Yamaha YZ125 Big Bore Kit Yamaha YZ134 Big Bore Kit Yamaha YZ144 Big Bore Kit YZ125 Big Bore Kit YZ134 Big Bore Kit YZ144 Big Bore Kit