I recently acquired an older PK Lindsay 25 HUE compressor powered by a Wisconsin S12D with a shared crankshaft. I have been unable to locate manuals or pars for the compressor though I found info and parts for the engine. I was able to get the engine running and after changing the oil in the compressor and firing it up, it built pressure in the tanks until the relief popped. I hooked a blowgun to it to see if it would maintain good flow and the pressure continually dropped. At this time the manual unloader levers on the cylinders had no tension on them when engaged which led me to look at the pilot valve. The pilot valve was corroded and gummed up inside. I cleaned it and reinstalled it to see if anything changed. The compressor now unloads at 95psi but pressure drops to 40psi and does not build back up. The manual levers have tension if you try to engage them. After shutting the compressor down you can hear air escaping from the pilot valve until the pressure gets to around 15psi. With the lack of parts for this compressor (and the voltage regulator on the engine needs replacint) I don't want to spend money on parts if it is not going to be useful without a rebuild. My thought is that a new pilot valve for the unloaders may fix the problem unless the compressor is loosing compression when it heats up.