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Old 10-25-2020, 02:52 PM   #1
Hux
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Onan 4000 shuts down and won't restart

I have an Onan 4000 4KYFA-26100P Spec P that won’t run for more than about 20 seconds. I’ve installed a new fuel filter, fuel pump, air filter, spark plug, and carburetor. The fuel pump is putting out 4 psi. As best I can tell, the float valve is working. I’ve pulled the spark plug and grounded it and see a spark. I also hooked up my old strobe, which I haven’t used in about 30 years, and it is blinking. If I let the generator stand for a day or 2 it will start and run for maybe 20 seconds, then quit. It will not start again after that unless I wait a day or 2. Anybody know what is wrong?
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Old 10-25-2020, 03:05 PM   #2
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Is the spark there when it stops and won't start?
Sometimes the oil level switch can be touchy, your oil level is proper? Also what error code does the status indicator light on the Control Switch flash?
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Old 10-29-2020, 09:10 PM   #3
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Thanks,
Yeh, guess what it still has spark. Fuel filter and pump and carburetor were new, so what could be wrong, fuel-wise. I sprayed starter fluid in and it wouldn't start, so I figured it had to be spark. Well it's not. Apparently it floods.
I've noticed the new carburetor has a little screw which is apparently a jet that my last 2 carburetors didn't have. What the hell is that? They had plugs. I haven't figured out how to paste a picture of it yet.
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Old 10-29-2020, 09:27 PM   #4
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Have you looked to see if the oil level is at full? Most generators will shut down if it's too low.
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Old 10-29-2020, 10:17 PM   #5
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Two things come to mind. Do you have more than 1/4 tank of gas? Next, did you check the oil level? If so, I would change the low oil pressure switch. Last and the ugly, it could be the control board. You have changed all the other normal stuff. Just my 2 cents worth. Good luck. Please post the fix.
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Old 10-29-2020, 11:18 PM   #6
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Do you get a blink code on the LED when it shuts down?
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Old 10-30-2020, 12:10 PM   #7
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Quote:
Originally Posted by Hux View Post
I've noticed the new carburetor has a little screw which is apparently a jet that my last 2 carburetors didn't have. What the hell is that? They had plugs.
The "plugs" only cover the screw underneath, it usually is a soft metal that can be pried away. Your new jet screws need to be turned out a specific amount, did you follow the manufactures directions for that?

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Originally Posted by Hux View Post
I haven't figured out how to paste a picture of it yet.
https://www.irv2.com/forums/f62/forums-101-posting-photos-accounts-basics-49134.html#post477709
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Old 10-30-2020, 12:33 PM   #8
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The manual states to replace the carb, NOT to make adjustments... balderdash!
The best I can say is turn it in (CW) and then 1¼ turns out for the initial adjustment, then fine tune when running. But ONLY if you know what you are doing, too lean and then you will develop a hole in a piston.
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Old 10-30-2020, 12:42 PM   #9
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You should NEVER randomly adjust the idle screw on an Onan generator, because these generators are designed to use the high speed screw for all adjustment, since they are designed to run at a constant 3600 rpms.


For the correct procedure refer to the old 1997 KY service manual http://www.skilledcrafting.com/onanf...0(02-1997).pdf


Which came out before the EPA mandated sealed carburetors
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Old 10-31-2020, 11:07 AM   #10
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Wondering if you got your generator fixed
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Old 11-03-2020, 08:09 PM   #11
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Onan 4000 shuts down and won't restart

There is no doubt my new carburetor was flooding. I should have realized that earlier. When I would pull the plug my hands would get gasoline all over them. I thought maybe it got sucked in after the spark quit. Not that much gas. Note, the spark plug being upside down fills up with gas. Maybe the float had a leak and wasn't shutting off the fuel. One last time, I pulled the bowl off. The float floated, the main jet looked a little funny though (the jet didn't appear to be inserted as deeply), so I replaced my new bowl with an old one. That appears to have fixed it. So I'm pretty sure my new carburetor was the problem. The generator ran for about 5 minutes before I had to quit and do something else. Previously, it didn't run more than about 20 seconds. Tomorrow, I will try to use my killawatt meter to adjust it and see if it will run for a hour or so. I'm kind of upset about the new carb.
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Old 11-03-2020, 09:29 PM   #12
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I just reread your initial post, 4 psi from the fuel pump seems high, I think Onan calls for 3.5 psi max, or else carburetor flooding may occur.


Did you use genuine Onan fuel pump and carburetor?
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Old 11-03-2020, 10:07 PM   #13
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If the choke was sticking closed that would make it run super rich also.
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Old 11-04-2020, 08:57 AM   #14
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Onan 4000 shuts down and won't restart

I thought the manual said between 3 and 5 psi on the fuel pump. I'll look again. I'm quite sure the choke wasn't the problem. Nor was oil or gasoline. In fact, I think I may add a little oil. I pulled some out, down to the middle of the dip stick. I had checked my float valve by turning the carb upside down and blowing on the intake, so possibly the float wasn't floating. In turned out it was. I held it underwater. So, the only thing I changed was the main jet, and that appears to have worked. I'll find out today. Interestingly, I blew into my fuel pressure gage also and couldn't get more than 1 psi, so I guess blowing on the intake didn't test it for 4 psi.
I pried a soft plug off an old carb and the screw was 1 1/4 turns out. It looks like oldweb was right. I have already backed it out more than 1 1/4. I don't want to burn a hole in my piston. Sorry EPA.
It looks like the main jet is pressed into the bottom of the fuel bowl from the back, and the new one wasn't pressed in all the way. It took me too long to diagnose, so Amazon won't take it back.
Thank you so much everybody for your help.
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