Replacement American Made Brass Air Syle Throttle Control for Kohler KD420 9 HP Gas Air Compressor For Use With Kohler Engines This valve controls the engine throttle speed on gas powered air compressors when used in conjunction with a pilot / unloader valve. This is the standard size valve that controls Kolher engines 9 HP. This is mounted next to the throttle arm on the engine and an air line is used from the pilot valve to control the engine speed. Valve Thread Size: 1/4" compression For Use With Kohler Engines Replacement American Made Brass Air Syle Throttle Control for Kohler KD420 9 HP Gas Air Compressor. For Use With Kohler Engines. This valve controls the engine throttle speed on gas powered air compressors when used in conjunction with a pilot / unloader valve. This is the standard size valve that controls Kohler engines 9 HP. This is mounted next to the throttle arm on the engine and an air line is used from the pilot valve to control the engine speed. Valve Thread Size: 1/4" compression For Use With Kolher Engines Up To 9 Horsepower.