Low pressure trying to build up then cuts down as if you were pulling trigger on and off

SOURCE: honda pressure washer cuts out when lance trigger released.

You most likely need to set your valve clearances. If it is hard to pull over or the recoil snaps back after starting your valves need to be set for sure. This may not be the entire problem but it is a good start. Also change the spark plug, a bad plug will cause odd problems and is too cheap not to eliminate as a source. In addition check your fuel, pour a little out into a white container (I like spray paint can caps for this) and look at the color. If it is yellow to orange it is bad. You can pour it into you car, the car electronic sensors will compinsate for it quality but a small engine can't. Use a NGK BP6ES or BPR6ES plug.
You need:
Feeler gages
10mm open end wrench
14mm open end wrench
1 long shaft screw driver or rod
1 spark plug socket and ratchet

Remove the spark plug and the valve cover. Pull the recoil over slowly until the intake valve opens (intake is closes to the carb and it will go down when it opens). Now put your long screwdrive down the spark plug hole. Slow pull the engine over until the screwdriver handle is at it highest point, this is top dead center. It may take a few attempts. Now check your valve clearance between the rockers and the top of the valve. The intake should be .006 and the exhaust .008, both can be +/- .001. To adjust: hold the large nut with the 14mm then loosen the small one with the 10mm. Lefty loosey. Now turn your large nut until you get the correct setting and then tighten the small one the lock it in. It may take a few attempts and alway reverify your setting after you lock it down. Once done, find top dead center again and reverify. Now your valves are set.

SOURCE: Kracher k3 97, low pressure

your pressure relief valve is stuck open. try adjusting the nut shaped stem on the front of the valve to see if you can unstick it. if not you'll have to take apart and clean.

SOURCE: builds up to much pressure in hose and stalls engine

Sounds like the unloader is not working. try replacing it and see if that helps.

SOURCE: Pressure washer lacks pressure initially?

Dear allbusiness9,
This problem is most probably due to a faulty Spill Valve( also called Control Valve). When the gun is released the spill valve is compressed and it either closes a micro switch or just opens from the bottom and keeps the water circulating. All spill valves keep the water circulating from the bottom part. Now when the gun is pulled (opened)...the spill valve extends and closes the bottom part, and thus water goes out of the nozzel. When you work with no nozzel, there is enough water flow to close the bottom part of the spill valve. So when the nozzel is placed back there is no chance that the bottom part leaks water. When the gun is started with the nozzel....the bottom part of a FAULTY spill valve,..will colapse and pressure drops. So to fix the fault you must change the Spill Valve. In some occasions, I also found that suction valves give this problem. A faulty sucktion valve will colapse under high pressure, and lets water pass the other way round.
But in my opinion and experience, your problem is in the Spill Valve.
Regards,
Fulltech.

SOURCE: Pressure pulsating when pulling trigger

you have a restriction in the nozzle end of the lance. clean with paper clip.
if not you have some dirt in the pump head valves which need cleaning