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post #1 of 17 Old 01-08-2019, 11:49 AM Thread Starter
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Generac pressure washer runs high rpm

I picked up a free pressure washer a while back, and it had sat for years. I assumed the water pump was shot, so I wanted to test out the motor before looking at the pump. The unit is a Generac 2100 psi residential washer with a Briggs Quantum 12000 series engine (6hp). I removed the pump and set aside. I cleaned out the fuel system, rebuilt the carb and got it running smooth. But it is running at around 4000 rpm, even with the throttle plate closed. The throttle lever itself doesn't do anything, except for shorting out at the stop position. I thought at first it was a throttle/governor/linkage issue, but everything appears correct. And as I said, the throttle is completely closed. Forcing the throttle plate open, by pulling against the governor, raises the rpms even higher. I keep thinking something simple is wrong. Do these machines run faster without the resistance of the water pump?

Thanks.
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post #2 of 17 Old 01-08-2019, 03:56 PM
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Re: Generac pressure washer runs high rpm

No, they should have a governor to maintain engine speed. If you can visually see the throttle plate closed in the carb (as in, blocking airflow in the carb), and it's still running at 4K rpm, something is wrong with the engine (most likely the carb, but possibly somewhere else).
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post #3 of 17 Old 01-08-2019, 05:32 PM Thread Starter
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Re: Generac pressure washer runs high rpm

thanks for response Dave. Yes I can see that the throttle plate is closed when running, the tab is against the stop on the carb body (where an adjust screw would be if this had one). This one has me baffled. Here is pic of the carb (I've had it off a few times now). It is in the almost fully closed position here from what I can tell. Is the plate installed incorrectly? It seems correct.
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post #4 of 17 Old 01-08-2019, 08:35 PM
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Re: Generac pressure washer runs high rpm

Are you saying that you cannot make it idle slow manually forcing the butterfly closed with your fingers????

If so and someone has monkeyed with the throttle butterfly, some are oval shaped or slightly offset in their mounting to the shaft and have to be orentated (put back) back in their correct factory position. Appears maybe that one is still open too much for a non-loaded engine.

I always make a witness mark on throttle butterflys before dicking with them in any way, especially if I'm going to remove them. (so as I can re-install exactly as they were before)
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post #5 of 17 Old 01-08-2019, 09:01 PM Thread Starter
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Re: Generac pressure washer runs high rpm

Forest Gump: yes, I can hold the throttle shaft closed and the engine still runs at 4000 rpm. The picture I posted was just me holding the carb loosely, the throttle was not fully closed. When it did close all the way, I'm not sure if it made a perfect seal with the inner body of the carb, though I don't know if they ever do. The orientation of the throttle plate appears to match all the carb repair pictures I could find, and the parts drawing as well.

Even if the plate is slightly off when in the closed position, shouldn't that just bring up idle a bit? WOT has the plate parallel to air flow, and should not be affected much if the plate is installed incorrectly.

This is just bugging me, it has to be something simple, there just isn't that much to these motors. Ugh.

Thanks for the comments.
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post #6 of 17 Old 01-09-2019, 07:09 AM
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Re: Generac pressure washer runs high rpm

Yep, strange. You might give use some more engine ID numbers, but in the meantime

Look at this picture carefully of a carb similiar to yours. (for a 6hp Briggs power washer motor)

Note that the throttle butterfly in this picture is not showing the large holes in it like your picture of the THROTTLE butterfly.. the choke butterfly has the holes in it..

Strange. Either replace the carb or trying closing the holes in the THROTTLE BUTTERFLY.

https://www.ebay.com/itm/Carburetor-...frcectupt=true

Appears maybe you have inherited a motor that some Bubba has been licking on. Has to be too much AIR going through the carb throat if the throttle butterfly is COMPLETELY CLOSED when you hold it manually closed.

Last edited by Forest Gump; 01-09-2019 at 07:17 AM.
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post #7 of 17 Old 01-09-2019, 10:00 AM Thread Starter
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Re: Generac pressure washer runs high rpm

yep. something is amiss. I thought all along this carb was behaving like it was improperly jetted. So I went back to the engine parts listings/diagrams and looked at the carb details again. There are 3 types listed for this series engine: auto-choke, primer system, and choke. This engine is no primer and manual choke. But the diagram shows it should have an idle jet, and this one does not. And all 3 have different main jets. So I think this may be the wrong carb, and/or wrong main jet too. All other internal parts appear to be the same, including the throttle plate and shaft.

Hopefully this Bubba can figure this out, (inexpensively).
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post #8 of 17 Old 01-09-2019, 10:53 AM
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Re: Generac pressure washer runs high rpm

I'd try loosening the throttle plate screw some & manually pushing the plate "more closed".
Retighten the screw.

With no load, it doesn't take a lot of fuel/air to run at high RPM.
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post #9 of 17 Old 01-09-2019, 03:33 PM Thread Starter
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Re: Generac pressure washer runs high rpm

Well I got the used pressure water motor running again. Turns out the throttle plate had been installed backwards. I reversed it to see if it would "seat" better, and it did. So I tried it, and it settled in to a more normal rpm range. It is running now at 3500 rpm, which may be a bit high, so I will probably drop it a bit by adjusting the governor linkages and/or spring. I'll add some more gas, and run some Seafoam through it just to clean out any old deposits. Then I can drop the rpms a bit, and put away till spring. In the meantime, I'll look for a replacement water pump.

Thanks all for the suggestions. Note that the Briggs part diagram for this carb did show the throttle plate in the incorrect position (180 deg out). It's not really an assembly diagram, but the way the part is shown is apparently not how it ends up assembled, so I can't really fault someone else for having it this way.

Every time I think I know a bit more about small engines, I find out how much less I really do know. Thanks again.
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post #10 of 17 Old 01-09-2019, 03:37 PM
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Re: Generac pressure washer runs high rpm

Good stuff. Thanks for posting what the fix was.

And 3500 rpm isn't necessarily too high, these engines are generally rated up to 3600 rpm, and then manufacturers (like Generac) will choose an rpm based on application.
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post #11 of 17 Old 01-09-2019, 03:45 PM Thread Starter
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Re: Generac pressure washer runs high rpm

Thanks Dave. You're right that 3500 rpm may be ok. I'll probably just leave it for now and see how it runs with a load. I'm wondering if I can find a used replacement pump that is repairable, as opposed to a new but not repairable one. My whole goal on this effort is to keep cost down, since this is only a cheaper residential unit, even if I have to do a little more work on it.
.
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post #12 of 17 Old 01-09-2019, 07:18 PM
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Re: Generac pressure washer runs high rpm

If you don't find a reasonable pump some of them Pressure waher engines make really good donor engines for other equipment, especially if it's a Horiz shaft they will bolt onto rototillers, wood splitters ,etc.
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post #13 of 17 Old 01-11-2019, 09:06 PM
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Re: Generac pressure washer runs high rpm

PaulM12
find the book for your washer/motor. it should tell how fast it needs to run

john
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post #14 of 17 Old 01-11-2019, 09:40 PM Thread Starter
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Re: Generac pressure washer runs high rpm

Forest: its a vertical shaft, so not quite as good of a donor engine. And I really just want to get a (cheap) pressure washer to use.
John: I have downloaded the washer user manual and parts manual, and the engine user manual and none list the speed. I have also looked through a few Briggs spec manuals trying to cross reference without any luck. I'm not too worried about this, if I get a pump working, I'll try out at the current speed and go from there.

Thanks all.
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post #15 of 17 Old 01-12-2019, 01:16 PM
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Re: Generac pressure washer runs high rpm

The vertical shaft pressure washer engines have a cast iron flywheel,so they'll run without anything on the crank,unlike a push mower engine,that needs a blade to act as a flywheel..I have got the flywheel off a few blown up Briggs pressure washers and they happened to fit a push mower engine that had an aluminum flywheel,that allowed me to use them to power other things..while not as versatile as a horizontal engine,the verticals aren't worthless either,as long as they have the heavy flywheel..one could propel a riding mower well enough to use as a yard mule,but maybe not be powerful enough to mow with..

I got a Campell-Housefield pressure washer a friend was tossing away because the pump got frozen and cracked during the winter,he failed to drain it and put anti-freeze in it--I put a GM alternator on it instead of the pump,I use it to boost low batteries on tractors and my diesel pickup in the winter..it has a Briggs 6.5 HP vertical shaft on it..


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