Honda5.0 hp on a karcher 2400 psi. I put a new unloader valve in it and it wont build pressure. when I pull the trigger I get a stream of low pressure. how can I adjust the unloader valve.

Things to check:
1) is water coming out of the bottom of the pump or is the oil in the crankcase high level and milky yellow. If so your seals are bad.

2) Your check valves might not be seating properly. A couple of fouled check vavles will cause either no pressure or pulsing pressure. A good inlet water strainer keeps foreign matter out of valves. But valves do wear out and get build up that keeps them from working right.

3) Your unloader valve might be worn or fouled. Bad unloader would usually show as low pressure ( but more than hose pressure) or low volume out the trigger nozzle.

Valves are your most likely problem.

I would have to agree with your service department. The unloader valve works like this, When you press the trigger it closes and allows the water to build pressure through the pump. When you let off the trigger the valve opens and by-passes the water through the pump so you don't damge the pump. If this valve is sticking and remaining open the pressure will not build. You can remove this valve and clean relubricate with white lithium grease just a coating and this should clear up your problem. Check the port that the valve sits in and if you see gunk just clean with carburetor cleaner and blow it out with air compressor. A new unloader valve can cost between $40.00 - $60.00. Try to clean first before you buy a new one. The valve is usually located near the outlet that you connect your pressure hose to. If you can't find it go to jackssmallenginerepair.com and do a parts look up for your machine and you will see where this valve is located. Hope this helps.

Your unloader valve is sticking, take a look at the attached link for information on how to repair the problem.

Hi, Karcher calls the unloader valve a spill valve,
this is a link to a full drawing/parts listing , and your fault description might well be a sticking /seized unloader(spill ) valve hope this helps
http://www.pressureparts.com/ManualViewPage.aspx?Manual=/mmDEV/PDF/karcherparts/g2500vh.pdf

the part number is on page 9 of the drawing
spill valve 45910400
hope this helps , we usually use some good quality silicone grease to lube the valve ,

It sounds to me like the unloader valve is bypassing internally.

I have the same problem. This is the responce for Karcher......

The unloader valve may be sticking, or is dirty. It probably needs to be cleaned and may need to be replaced, it is inexpensive. It gets a lot of use, but extends the life of the pump. The function of the unloader is to allow the machine to run in a bypass mode while the trigger of the gun is closed. First, a lack of high pressure can be caused by: 1. Insufficient water feeding to the unit, so check that the water is turned on all the way and that there are no kinks in the hose. 2. The inlet filter may be clogged. (it will need to be removed and thoroughly cleaned). 3. An internal water leak. 4.Also, low pressure can be caused by worn spray tips. If you have checked the first three with no resolution, the problem is internal and could be as simple as a sticking unloader valve. If you are mechanically inclined, you can clean this valve yourself and greasing the o-rings (use lithium based grease), or take it to a local service center. You do not need to take the pump apar
t. The unloader valve is located under the cover, and is secured with 2 bolts. (Use needle nose pliers to remove the valve) For those units with pressure and volume controls, the unloader is located under the pressure and volume control knobs themselves. Do not take any other bolts off or you will open the pump and lose the pump's oil.

Note: Lithium based grease will prevent future failure of the unloader valve.

Also, check websites such as fixya.com for tips and how-to info particularly on cleaning the unloader valve. Be sure to use lithium grease if you reassemble it.
I am going to check the manuel to see where it's at

unloader valve sticking in the pump head. remove unloader valve/ pressure reducing valve as per parts manual.

It will probably be caked up in white crystal type deposits if its an aluminium pump head. clean off the deposits and inspect the 'o' rings. if 'o' rings ok , apply silicon grease and refit.

It could also be a partially blocked lance jet not allowing enough water to come out of the lance if it is a flow sensitive unloader valve.

The Karcher K2400HH and G2400HH do not have an unloader valve, they have a spill valve which is located under the black cap on top of the pump.

The spill valve needs to be removed and the side walls of the hole it sits in need to be wire brushed to remove deposits. then you can put it back in and put the pump back together.

Your uplift injector valve in the water pump is sticking. You need to remove this part. Lube the top o-ring only with a water proof grease. Reinstall this part. You will be up and running again.

You need to use needle nose vise grip tool to easily remove the valve. You need to grind down the vise grip tool to fit the opening where the valve is installed.

To prevent this problem from reoccuring use a pump guard additive.

www.paddockdrayage.com/karcher/