Chinese Scooter 49cc to 80cc Big Bore Kit QMB139

Want real gains from your QMB139 / GY6 50? This upgrade bumps your stock 49cc up to a true 80cc — giving you way better takeoff, less struggle on hills, and a scooter that finally keeps up with traffic instead of holding it up.

The Details

We tested tons of cheap big bore kits — and most failed over time. This one is reliable, hits harder off the line, and gives you the muscle to climb hills without bogging. Installation is simple with basic tools, and we even have step-by-step videos to guide you.

To really wake it up, add the big-bore carb: CLICK HERE

Need torque specs during install? GY6 torque settings click here

Important Things to Note

• Fits QMB139 / 139QMB / GY6 50 (4-stroke) engines
• Upgrading the cam is recommended for long-term reliability — stock bearings are weak
• Break in the new cylinder before going full throttle
• A fresh spark plug is always a smart idea with performance upgrades

Performance parts are not returnable. Extra power can reduce OEM reliability if not installed/tuned correctly.

Will this fit your engine?

Want the full 45-minute install walkthrough? Click here

What's Included

• 80cc big bore cylinder + piston
• Gaskets and install hardware