Electric pressure washer looses pressure after 8 sec.

The first thing I'd try is some lubrication.

lubricate which parts? Do I need to unscrew the main body casing? thanks

See if your problem is listed under the Simoniz FAQ's

Typical problem with cheap universal motors is that the brush holder is made of plastic. So, you overload it, it runs hot. After a while the plastic brush holder melts where it contacts the metal. It's still running fine, cause it's hot. But when you let off the trigger, the plastic that's oozed onto the brush hardens. Now the brush is frozen and there's lots of arcing and sparking on the commutator. If you let this go on, it really tears up the commutator and the brush. If you catch it early, you can free the brush and shine up the commutator.

The fix is to disassemble the motor and free the brushes. Technique depends somewhat on the construction. On my chainsaw, I use a big soldering iron to heat the metal just enough to free the brush. Then take half an hour with a tiny rat-tail file and xacto knife to get all the plastic out. Works fine until I forget and try to cut a limb too big and it starts all over again. Same problem with the electric lawn edger.

mike

Make sure the water inlet is not restricted by blocked filter sometimes fitted in water inlet coupling , or hose is not being kinked . When the volume of water going in is restricted the outlet high pressure cannot be maintained, think of 'Pressure times volume equals a constant '