OK kart engines have a maximum specified carburettor diameter of 24 mm.
The restriction belongs to the CIK-FIA technical regulations for Original Kart, the senior direct-drive class. OK engines are 125cc, water-cooled two-stroke units with mixed lubrication, and their screw carburettors may not exceed the stated 24 mm diameter.
Carburettor dimensions matter because the carburettor controls the flow of the air-and-fuel mixture into the engine. A larger opening could allow greater airflow and potentially more power, so a maximum diameter helps keep engines within the class’s intended performance and reduce advantages based on engine preparation.
This figure is often confused with specifications from other karting categories. KZ gearbox karts, for example, use a different engine package and have a larger maximum carburettor diameter in their regulations. The 24 mm limit applies specifically to the senior OK specification, not to every 125cc racing kart.