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The Athena 105cc Big Bore cylinder kit is designed for competitive motocross riders looking to upgrade their Yamaha YZ 85 for increased power and improved throttle response. By expanding the displacement to 105cc, this kit delivers a more dynamic and lively engine character, though it requires precise engine tuning and professional installation to ensure optimal long-term performance and reliability.
| Model Part Number | P400485100038 |
|---|---|
| Brand | Athena |
The kit features a 53mm bore, resulting in a displacement of 105cc.
This is a bolt-on kit, but it is highly recommended to adjust your carburetor jetting to accommodate the increased displacement.
The Athena 105cc kit operates at a compression ratio of 13.8:1.
No, this is a performance kit intended for closed-course motocross competition only.
Due to the high compression ratio, high-octane pump gas or race fuel is recommended to prevent engine damage.
Verify that the timing is correct and check the spark plug for fouling, which can occur during the initial tuning phase.
Ensure you are using the correct octane fuel and check that your carburetor jetting is rich enough to compensate for the increased displacement.
Check the cylinder compression and inspect the air filter; ensure your pre-mix ratio is correct for the new engine configuration.
This kit is designed specifically for the Yamaha YZ 85 and is not a universal part. Professional installation is highly recommended to ensure proper timing, squish clearance, and gasket sealing. After installation, perform a proper engine break-in procedure by varying throttle inputs and avoiding sustained high RPMs for the first tank of fuel. Regular maintenance includes monitoring for coolant leaks, checking the head bolt torque periodically, and inspecting the air filter to ensure no debris enters the higher-performance combustion chamber. Always use high-quality two-stroke oil to match the increased thermal demands of the larger cylinder.
