Yamaha off-road motorcycle // sport atv athena 300cc big bore kit
Engine / performance
This 300cc Big Bore Kit by Athena increases YZ250 displacement to 293cc. Cylinder is nickel-carbide plated with enlarged water passages for exceptional durability and performance. Bore increased to 72mm (stock is 66.4mm); stroke remains the same as stock (72mm). 15:1 compression ratio. Forged, domed piston. No case machining necessary. Kit includes cylinder, head, piston, rings, pin, clips, power valve assembly, and all required gaskets.
Jetting Recommendations:
Slow Jet: 52
Air Screw: 2-1/2 turns out
Main Jet: 175-178
Needle: NBLE, 3rd notch
Yamaha off-road motorcycle // sport atv athena 300cc big bore kit
Yamaha off-road motorcycle // sport atv athena 300cc big bore kit
