It is a one year old Karcher K3.91 M electric pressure washer. It was stored in garage over the winter without any anti-freeze protection. The motor pulses on/off when the jet pipe is in high pressure setting. It functions fine with the rotary nozzle, however, I'm not certain if the water pressure is as high as when it was new. It seems that the motor periodically power cycled in a condition that the pressure load exceed a certain threshold. Please help. Thanks!

Ok, figured that would possibly be the problem. There are three O rings that fit inside the brass manifold. They are rubber O rings inside a round plastic housing. Since there doesnt appear to be any oil leaking in the water, I have to assume the oil seals are ok and just these plastic encased O rings need to be replaced. My pump is on a vertical shaft. Will the new O rings need to be facing with the rubber side up or the plastic side up? Thanks

Hi, I have a six year old Karcher K360M, used only once a year. This year, when I was washing my house, the first four hours were no problem. But then, I had set it down and the motor just turned on without pulling the trigger. And when I pulled the trigger, there was no pressure. It was basically just a running motor. It continued to run even when I tried turning the switch off. The only way to turn it off was to unplug it. I tried it the next day when it was cooled off, and as soon as I plugged it in, the motor automatically came on and again, and I had to unplug it to stop the motor. Does anyone know anything about these power washers? Could the switch have gone bad, or do you have any other ideas as to what would cause it to keep running with no pressure? I don't want to start spending money on parts without having an idea of what the problem might be. Any help would be appreciated. Tim

My problem is solved! It was the gas cap. Had the same exact problem as reported by rszanti in October 2005 (the OP). I won't describe my problem because rszanti's first paragraph at the top of this post describes it verbatim. I will say that I felt my problem was a fuel problem because of how easy it would start after each stall. If the problem was heat related, I would expect more time would be required to let things cool down before it would start again. >Craftsman 3100 PSI Pressure Washer Model 580.752080 purchase new in 2007 >Briggs & Stratton 121012-0123-B1 900 Series Single Cylinder OHV 4 cycle (no fuel pump or filter) >No more than 20 hours of use on it. This is how I diagnosed the problem: The gas tank has a shut off valve. Closed that and disconnected the fuel hose from the carb. Removed the gas tank from the pressure washer. Held the tank over a gas container and opened the shut off valve. Gas started draining and then got slower and slower until it stopped draining, even though the tank was still full. Loosened the cap and the gas started flowing again. After draining the tank, I tightened the gas cap and put compressed air at the fuel hose. No air leak. So my guess as to what was happening is: The carb bowl has gas and no vacuum exists in the tank. On first start, engine runs for about 5 minutes under full load and then stalls. The stall is caused because vacuum has built up in the tank and there is not enough fuel flow to serve the engine's need under load. The carb bowl empties and the engine stalls. Now the engine sits for a minute. Gas trickles into the carb bowl. On second start, the engine fires up but sucks the carb bowl dry again. (By the way, it will run for a long time if not under load. Probably because it doesn't require as much fuel flow.) I inspected the cap design closely and it has no vent hole. I'm not sure why the cap worked and now it doesn't. Guessing there was something there that prevented the cap from screwing down too far, and over time it wore down. I didn't see anything on the tank either that would suggest a design for venting. Anyway, now I screw on the cap so it is almost loose and the pressure washer has worked all afternoon under full load with no stalls. Go figure.