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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 26056
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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I have a Karcher 3.91M that is surging. It worked the other

Customer Question

I have a Karcher 3.91M that is surging. It worked the other day for an hour, and then after putting the wand down for 5 minutes, it started surging. I've tried everything discussed everywhere, sonitmlooks.like it might be the unloader valve. I have a parts diagram, but I am not sure what the unloader valve is - can you help? I can send you the pdf.
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Submitted: 6 months ago.
Category: Small Engine
Expert:  Curtis B. replied 6 months ago.

Is the inlet strainer clean? If so, it can be the unloader. The unloader my also be called spill valve.

Expert:  Curtis B. replied 6 months ago.

# ***** and 8 make up the spill valve.

Customer: replied 6 months ago.
Am I correct in seeing that they only provide part 8, and not part 7? And part 8 is $60, before shipping.Might not be worth fixing
Expert:  Curtis B. replied 6 months ago.

The parts are expensive,but cleaning the valve may be all that is required. If it does not work after cleaning, I would not recommend spending any money on it!

Customer: replied 6 months ago.
Ok I pulled it apartWithout completely disassembling b-7 & b-8, they look like they need a good cleaning. There is also a picture of the throat for the unloader valve, and it looks pretty dirty, as well. Do you agree?I also opened the control head - does it need any cleaning?I've attached pics of all.What should be used to clean the various parts? What grease should be used?Also, there is a broken O-ring, which I think was from the electrical connector...Where would I get that?
Expert:  Curtis B. replied 6 months ago.

Just use a light grease, like vaseline. and auto supply carry an assortment of various size o'rings.

Customer: replied 6 months ago.
You agree I take it that b-7 & b-8 and the throat are dirty? Any thoughts about the conto head? Does that grease look ok?
Expert:  Curtis B. replied 6 months ago.

Yes, i see no problem with the grease in the pump section.

Customer: replied 6 months ago.
Hi Curtis I haven't had a chance to reassemble the pwr washer so pls give me a day or two
Expert:  Curtis B. replied 6 months ago.

Take all the time you need! Thanks for reply.

Customer: replied 6 months ago.
I'll get the time to try out the repairs today and let you know
Expert:  Curtis B. replied 6 months ago.

We had 4 more inches today!

Customer: replied 6 months ago.
Ok so I was able to ensure it was all cleaned and got it reassembled. It appears to wash at good pressure, but now does not shut off when the trigger is released (as soon as the power switch is turned on, it runs and runs until powered off).One thing I noticed is that the plunger for B-8 (exits at bottom of hihh pressure side portion of pump housing) appears to press in a contact switch on the electrical housing unit.Another thing was the nipple, and thus the housing for B-7 is not cocked at 90deg. to the pump housing, the way it was prior to disassembly. I tried to spin it, but it was VERY tight, and I was worried the nipple would break...if you look at the pic I attached, it looks like there are "flow ports", that are at 0/360,90,180,270 degrees (I circled one of the openings that I suspect is a flow port)Is it imperative I am able to spin the B-7 nipple to a 90 or 180 deg position to allow this port some type of flow access, and thus depress the plunger to shut off the pump?Trying to remove B-7 again, as it's quite stiff, may break the nipple. This nipple is for pulling from the soap/solution container. If the nipple breaks, other than losing the ability to use it with solutions, is there any issue?
Expert:  Curtis B. replied 6 months ago.

The nipple houses the check valve for the washer solution. As long as the nipple or hole is shut, it will not affect operation of the washer. I see no pictures attached. ?? The plunger you speak of does have to be able to push on the switch, or pump keeps pumping!

Customer: replied 6 months ago.
that txt was copied off a reply from me last night that went back to a no reply email for some reason...I'm trying to add the pic but getting error msgs
Expert:  Curtis B. replied 6 months ago.

Use the paperclip icon above the typing bar for attaching photos.

Customer: replied 6 months ago.
This mobile web app won't accept the jpegI just replied to the email - did you get it?
Expert:  Curtis B. replied 6 months ago.

If you send through email, the site gets the pictures. I have no access to your email address. I work from home as a contractor. Did you see what I said about the nipple and switch?

Customer: replied 6 months ago.
I think the "ports" are separate from the nipple, in terms of functionMaybe the plunger/valve is stiff and needs to be diassembled and re-lubricated?
Expert:  Curtis B. replied 6 months ago.

It does have to move to push and release the switch!

Customer: replied 6 months ago.
Ok I pulled it apart, cleaned it all again, and re greased the hi pressure side.It doesn't surge at all and runs nominally, but still won't shut off.:(When I reassembled it, the B-8 plunger was still very stiff to move, and seemed to be forced into the extended position by B-7.Not sure what else to do.
Expert:  Curtis B. replied 6 months ago.

Can it move at all? Switch needs very little travel to turn motor on and off. Or just let it pump pressure, and shut if off manually

Customer: replied 6 months ago.
It is very stiff...if it moves it is not much.If I use it and shut it off manually, will thw pump take abuse? If so, how much use will I get out of it?
Expert:  Curtis B. replied 6 months ago.

It will not hurt the pump, it is made to run continuously.

Customer: replied 6 months ago.
Ah ok sounds good then I think we are good much appreciated
Expert:  Curtis B. replied 6 months ago.

Thanks , please rate to close.

Customer: replied 6 months ago.
I'll be darned.I ordered a new B-7 found one for $20, and put it in. The machine worked well without surging, and the motor was stopping when powered on but without the trigger pressed, as designed.
But it started surging again, but in a faster cadence than before, after about 20 or 30 minutes of use.
I pulled it all apart, and while it looked good I cleaned and rely bed it all, but it still surges.
It no longer runs without the trigger pressed.Very frustrating. Thoughts?
Customer: replied 6 months ago.
Not "rely bed" - re-lubed
Expert:  Curtis B. replied 6 months ago.

The inlet screen hasn't become restricted from trash?

Customer: replied 6 months ago.
No that was the 1st thing I checked
Expert:  Curtis B. replied 6 months ago.

I don't know, I thought we were on the right track. I can opt out and see if anyone else will answer. Sorry.

Customer: replied 6 months ago.
Copy that
Do you think it's possible the high pressure hose has a clog? Maybe not, since it seems to work without surging right up until I turn the variable wand to almost complete high pressure.
Customer: replied 6 months ago.
Hi Curtis - Any status update?