KTM 300- Stock 36mm Carb vs 38mm PWM Carb = 52HP KTM 300- Stock 36mm Carb vs 38mm PWM Carb = 52HP Keihin 38mm PWM carb and a well tuned power valve can make huge gains in power. KTM 2-Stroke 250300 POWER VALVE TUNING -Picture Gallery