How to repair a karcher pressure washer keeps pulsing

SOURCE: trouble with Karcher Pressure washer

Dear Pgarciax,
It is important that you must have mentioned the model number of your Karcher. Just the same I can surely say that your machine's fault lies in the "SPILL VALVE"
When the gun is open and pressure is being produced, the spill valve is in a relaxed position. Also it has at the bottom a valve, which when pressure is produced it is closed. If this does not close due to dirt or corrosion, the pessure goes down. Now when you close the gun,pressure forces the spill valve down to close the electrical system. Now if the "o" rings of the spill valve are damaged, the machine will start going on and off while in stand-by. So if you know how to locate the Spill Valve, all one has to do is change it with a new one.
In some Karcher machines there are 2 spill valves. One regulates pressure and the other one is for switching off the machine when the gun is closed.
Low pressure could also be due to faulty suction or delivery valves. Most probably the suction valves.
But when saying that there are short interruptions while in stand by, I stick to the fact that the spill valve needs renewing.
Regards,
MG.

SOURCE: Karcher Pressure washer surging/pulsing

here is a troubleshooting link for Karcher products

http://www.the-power-washer-advisor.com/electric-pressure-washer-troubleshooting.html

SOURCE: Karcher Motor Pulese On and Off

hi mark, you do have a problem with the lance.
you need to disconnect the lance and straighten a paper clip and insert down the nozzle end.
use the machine to wash the dirt in the nozzle backward down the lance.
Dirt only in nozzle end.
if still no good, purchase some nozzle cleaners and file out nozzle very slightly.

SOURCE: Unloader Valve - Karcher Pressure Washer

where is the unloader valve locaed on a Briggs Stratton pressure washer?

SOURCE: I have a Karcher K5.55M The motor pulses and only 1/2 pressure

In the video link above, at 7 minutes,.. through to 7 minutes 8 seconds,.. the guy talks about a "minute crack in the cylinder head". He actually means to say "minute crack in the control head". This minute crack is the main reason for this common problem: the pulsating and some loss in pressure on a wide range of Karcher waterblasters.
I got a replacement control head from my local Karcher dealer for NZ$50 that fixed the problem,.. for now :-( The below picture has two red ovals around the cracks in the control head that are very hard to see. If Karcher made this control head from an aluminium casting, their product range would be a LOT better.