Direct-drive karts: 100cc karts (called Formula A and ICA) prevailed for almost 50 years. The current reference cylinder capacity is however 125cc. The increased capacity introduced with KF engines went along with the introduction of rev limiters. Switching over from 100cc engines to 125cc KF's has entailed very few changes as regards chassis design.
The KF engine idea arose as a result of two factors: first, the 100cc technique had arrived at the end of its cycle and the outrageous engine revs reached over 20,000 rpm!. That eventually made the engines fragile and extremely costly; secondly, the engine types used in Karting had to move towards more modernism, extra user-friendliness and more respect of the environment. To the cultural shock and heavy technical changes that a hasty switch over to 4-stroke would have entailed, the industrial partners, the distribution networks and most users have preferred the sustainable development of 2-stroke engines, in keeping with the modern priorities of societies. And the KF engine concept was born in 2007.
KF engines were not different from their predecessors only because of their increased cylinder-capacity as they also have the specificity to include a balancing shaft, an integrated water pump, an electric starter (Tag), a single-type centrifugal clutch, an ignition which includes a rev-limiter and, on the fastest versions, an exhaust valve also called “power valve”
The KF engines were replaced by the OK engines in 2016. The OK engine would keep the 125cc engine formula with a “power valve” on the fastest version. However the engines would go back being direct drive (no clutch and no starter motor) and are fitted with a decompression valve to aid starting.
