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Old 05-18-2018, 04:18 PM   #1
Join Date: Sep 2016
Location: Texas
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New Onan 4000 question

Teaman here. ............ I have been running the Onan generator about 20 min each month and all has been fine until lately the Gen will sputter and die after several minutes. Will crank and start later, but still only runs a short while. I immediately thought of water in the gas line or carb. But looking over the manuals, I have some question about the carb bowl drain. The diagram shows an arrow to just below the 'Altitude' adjust knob. And the manual says it is a screw.

I found a Philips screw at that location, but when I unscrewed it, it turned out to be a 'Needle Valve' type screw with a point end and a spring around it. It looks like some kind of mixture control or something. I took it all the way out and I saw only a little gas drip down.

Is this the real drain point, or am I monkeying around with something else? I put this screw back in and tightened down completely. Then I started the gen OK. But it again only run about a minute before chugging down.

Anybody got any experience with this generator? I could use the help.

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Old 05-18-2018, 08:59 PM   #2
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See pages 44 & 45 to assuage your concerns:

ILB ( | )
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Old 05-19-2018, 08:27 AM   #3
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I will throw out my limited experience with this generator.

My generator would run rough and surge a lot but did not die like yours does. There are some videos on the web regarding a seafoam cleaning. It involves removing the fuel line and running off a mixture of gas and seafoam for an hour or so. It made a big difference on my generator.

Later on, my generator got difficult to start. There is an arm that attaches to the carb that was sticky... I think that the choke did not engage. Perhaps your choke is stuck on all the time. I just wiggled the lever a few times and then it moved freely.

I hope this might help...
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Old 05-19-2018, 08:46 AM   #4
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Sounds like a fuel pump/filter/float problem. 2013 is pretty new and you have been running it. I would be surprised if it were water since the generator fuel connection is well above the bottom of the tank (1/4?). Can you hear a metallic sound from the fuel pump? If so it is starved or sucking air somewhere...or just bad. If you take the line off the carb and put it in a jar and have press and hold the stop switch down on the generator it will run the fuel pump and you can see if you are getting any fuel pressure to the carb.

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Old 05-19-2018, 08:59 AM   #5
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A needle valve like you removed should not be tightened down completely I would back it out between .75 and 1.5 turns and try again.

How old is the gas in the tank ? is there any sort of additive in it ?
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Old 05-19-2018, 10:19 AM   #6
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Teaman here. ............... Thanks for the replies. Funny thing. Yesterday I posted a reply to Duckogram and thanked him for his post and helpful tip. Now I can't find that reply on this thread? Guess it went somewhere else.

In any case he supplied me with a link to an Onan Gen. Manual. It had an illustration of the part of the carb. containing the Altitude control knob and a Phillips head screw in greater detail than the manual I was using. The arrow clearly pointed to that screw that I had loosened and taken out. So I was diddling with the correct 'drain' screw alright. I'l have to try that bowl drain routine again.

Thanks for those extra tips. I'l look into those angles soon. Maybe I have allowed the fuel to get contaminated with 'condensation' water. The MH has been sitting about six months, and I tried to run the truck engine and the Onan once each month. Maybe not enough. The manual from Duckogram said I should have run the gen. much longer each month.

The MH gasoline tank is about 3/4 full so there is enough room for air to allow the dreaded condensation to form. It was standard practice when flying airplanes to walk around pressing all the drain cocks on the wing tanks and the carb. before each flight. Sometimes a lot of water would dribble out before the gas would.
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Old 05-19-2018, 12:33 PM   #7
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The automatic choke linkage was stuck (off) on My 4000 with under 30 hours on it. Was very hard starting form day one. I fixed it by loosening the set screw on the choke assembly and turning the adjuster counter clockwise until the linkage released. When the engine is completely cool the linkage should move freely.
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Old 05-19-2018, 04:41 PM   #8
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I had a similar problem with my Onan 5500. Took it to a service center where they removed and cleaned the carb. It had sticky residue built up.

They suggested I run the genny 45 mins at least once per month. And, when you run it make sure there is a load like the AC. I do that now and the genny has been very reliable since then.


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Old 05-19-2018, 05:53 PM   #9
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Onan 4000

Add stabeliser in the gas tank (red Stuff)
if your gas is sitting more then 2 monts in the tank.
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Old 05-19-2018, 08:29 PM   #10
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it only use abt 1/2 gal a HR under no load need to run lot longer at least a HR w/AC on need load to keep carb clean

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