KTM65    They left the anti surge washer out from under the main jet. This causes a bad bog on landing after a jump. The std carby needle is too rich, buying a jet kit is best if racing. The plastic water pump gear waers fast- about 30-40 hours and need replacement. The stock gearing 14-48 is fine for heavier riders, light weight riders will need a 47. Extending the swing arm and forks makes the bike handle better at speed, and easier to ride ( for faster riders) This is the best 65cc bike for racing and KTM have done a really good job on the design in most areas. Extra power is easy to get, bigger carby, VH special exhaust is great, VHM head with powervalve adjuster,  CDI unit and you have a rocket! A very exciting bike to race when mods are done. The best 65 to race.

General problems- plastic waterpump gear wears fast, broken powervalves.(use the heavy duty one ) Oil in powervalve pressure chamber. Carbon in exhaust pressure outlet, use a cleaner oil. Water entering spark plug cap from pressure cleaning.  carb needle too rich, fouls plugs. Fit a jet kit.

2017-2020 KTM SX65 Powervalve

This is a 3 piece design ( like the Nihilo type) and can come apart . The powervalve hits in the bottom of the port sides , this slamming down damages the powervalve , But from 2017 you have a small threaded connector ( the 3rd piece) installed, we have had this piece fall back inside the engine and cause damage. Using the VHM powervalve and the special base is best. Take care when fitting.