The KTM sx50 needs to have the clutch speed set higher for racing MX or flat track. The clutch will be set at about 8 clicks from the factory, and this needs to be around 14-15 clicks to have the engagement speed of 8500 rpm to 9200 rpm. Use a Tacho best. This will cause more clutch wear and more heat inside the engine, but alot more power is gained and required for racing. The stock gearing is too low for most tracks, so moving to 12-40 gearing produces better laps times for mx and 12-38 for flat track is better.
After changing the clutch speed and the gearing then replacing the exhaust system will make the engine perform much better, as the stock exhaust is designed for the stock engine set up. HGS special exhausts make very good gains in power.
Jetting for fast riders, 50 pilot and 98-100 main jet needle on the 2nd clip , fuel screw at 2.5 turns out works well.
General bike design problems- clutch wear, Ignition stator failures, poor front forks, plastic water pump gear wears fast, engine performance for racing is down compared to the Cobra, the KTM engine is still using an old design half circle type crankshaft , the ignition timing is not adjustable and the cooling system is limited.
Race fuel works well. Spare parts easy to obtain in Australia. Porting work adds good power.