try taking your unloader valve out and either clean it really good or replace it if it is too gummed up.

either way, when you put it back in, be sure to coat it with either lithium grease or pump oil.

iowaguy,

My DH had the same problem with our gas powered Karcher Pressure Washer. He's very mechanical/engine savy and tried unsuccessfully for a couple of days to fix it.

He finally took it to an authorized Karcher service center and the guy knew immediately what was wrong with it. He re-honed the cylinder for the pressure control valve to make it smooth enough so it doesn't hang up.

The shop owner said almost every one of Karcher's pressure washers has this problem after a few hours of use (poor quality control). The cost was around $100 last year, but he also had broken motor mounts and something else fixed at the same time.

Haven't used it a whole lot since then, but hopefully this is a permanent fix.