100cc Short Case GY6 QMB139 Scooter Big Bore Racing Engine
This is the 100cc SHORT case scooter engine that fits scooters with short case 50cc engines.
This is the 4-Stroke complete engine, long crankcase. For the 100cc big bore engine we install the 50mm big bore cylinder and piston and a performance head in the engine.
The reason that your 50cc scooter engine is so weak and powerelsss is that your combustion chamber and piston is so small--only a little larger than a quarter. see pictures below. The power of your engine come from the explosions when the gasoline is ignited in the cylinder. The smaller the chamber the small the explosion and the less power. Compare to the 100cc big bore cylinder and piston kit you have double the volume of combustion chamber and thus far more power. see pictures below.