New to the PW world, northstar Honda 390 with 4k 3.5gpm cat pulsating, not enough pressure

Just picked up this machine as a second unit.
It’s a Honda 390 with CAT pump. 4k 3.5gpm.
Starts up great, but when using the wand, it definitely doesn’t have all the pressure it’s supposed to, and it kind of pulsates.
I’m new to this world, been pressure washing my own stuff for years, just now adding it to my list of services.

Other machine is a Honda 390 with AAA triplex pump 4k 4gpm and it has much more power with consistent stream…

Any idea on what my issue can be?

Been reading a lot, and this can be overwhelming to try to start off in this business, so much to learn, so much competition out there!

Thanks so much

What does it do without a tip in the wand?

I’ll check that out tomorrow AM. I didn’t test.

Do a bucket test, no tip. If it’s spot on and doesn’t surge, throw in a xxx3.5 tip and see what happens. Your tips might be undersized and screwing with your unloader. No tips smaller than 3.5 for that machine, xxx4 is closer to real world use after the hose loss. Did you set the unloader with a pressure gauge?

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Also, I should say the tips I suggested are for maximum pressure output on that machine. Fine for setting the unloader, but don’t go using those on anyone’s siding


It sounds like it may be starved for water. I know some of them have the little screen on the garden hose inlet fitting, the screen may be partially plugged.


I will read into setting the unloader. Thanks for the input. I’ll try tomorrow AM and report back with my findings. Much appreciated.

Did the bucket test.
It initially shoots s good stream for a second or 2, then starts to sputter… No tip in.
I took the unloader apart and cleaned everything and reinstalled, adjusted it as I keep spraying off and on. No change in the pulsating with the tip in. I tried multiple tips. 0004, 2504, etc.
The hose even vibrates like crazy at open throttle. Consistent pulsating in the stream with the tip in. Sputtering with tip out.

Any thoughts?

Too that screen out, it was pretty clean… Fully clothed and reinstalled, garden hose at be full pressure. My other 4k/4gpm works fine.

You either have a stuck check valve, cracked plunger, bad seals or a massive air leak.

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I ordered a pump rebuild kit, I guess I can start there.

It’s good to have a rebuild kit on standby but most of those kits don’t include check valves or plungers. So, if the kit you ordered doesn’t have those and one of those happens to be your issue you’re going to need to order those as well. Just pop the manifold off and have a look around in there. Check valves should move freely and seat correctly, plungers should not have ANY cracks in them (they’re typically extremely small and hard to see, inspect them thoroughly), unless the seals are so far gone that cavitation has crept up past the outermost seal, you won’t be able to see damaged seals unless you pull them. Keep track of the order you pulled them in and try not to damage them unless you’re going to replace them regardless.