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Old 04-05-2021, 05:25 PM   #1
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Generator carb

Is it possible to take off the carburator on the onan 4000? I know that you can't get a rebuild kit for it but we can't even get it off to work on the fool thing. 😡
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Old 04-05-2021, 05:46 PM   #2
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I don't know if this will help but there are numerous YouTube Videos on the issue.



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Old 04-05-2021, 06:50 PM   #3
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Thank you, but this guy does the same thing all the other videos do so far. He talks about taking it off but doesn't show how he got to that point. Just cuts away and *poof* it's off.

Still trying to find one that actually has it coming off and how they get to whatever bolt it is.
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Old 04-06-2021, 07:19 AM   #4
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I took the carb off my 4000 genset, over hauled it put it back on and have 100 hours on the set with out a whimper. I started it yesterday to test it before our three day trip starting today. The carb is not that hard to get off but it does require care and patience.

TAKE A PICTURE(S) OF EVERYTHING BEFORE YOU TAKE ANYTHING APART! Looking at the gen set in the lower left front is a Ford type solenoid switch. The black heavy gauge wire coming through the gen set case and bolted to the relay PROVIDES STARTING VOLTAGE TO THE GEN SET AND IT'S IS ALL WAYS HOT. THE ONLY WAY TO DISCONNECT IT FROM THE STARTING CIRCUIT IS TO DISCONNECT THE HOUSE BATTERY. TURNING OFF THE 12 VOLT SERVICE SWITCH WILL NOT DISCONNECT THE GENERATOR. Either at the battery or at the genset disconnect that cable. After that you can take the air filter cover off, tip the filter as much as you can to wiggle it out of the cover and set it aside. The air filter housing and the carburetor are held on with two 10mm bolts. The head of the bolts are at nine o'clock and three o'clock at the bottom of the housing. You'll need a quarter inch drive ratchet drive, the 10mm short socket and a quarter inch extension. As you move the carb out you'll see two light weight wire rods connected to the top of the carb, one is the throttle control and the other is the governor. Pay attention to and maybe take a picture of how the rods connect to the carb, it's simple but they are fragile. The red wire is the "automatic" choke. It connects to the carb by a spade connector. I spliced a much longer section of wire into that wire. It's way to short for you to work with. The black wire is the negative and simply clamps to the intake manifold. Before you take the carb apart gently screw the adjustment screws including the altitude adjustment screw all the way in. Then you'll know where to set them when you reassemble it. When taking it apart be very, very careful to not damage the gaskets. You can not replace them. When you reassemble use a gasoline grade gasket compound. I used ariosol carb cleaner. Reverse the process to put it back together It's a very simple carb, you won't have any trouble and you'll feel a sense of joy when you hit the starter and the genset light's up. One last thing. I have a brand new in the box Onan carburetor I can and will part with for cheap. I bought it before I took mine apart in case things awry. If you're interested let me know by private message.

Best regards
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Old 04-06-2021, 08:10 AM   #5
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I do not have an Onan. Does the bolt have a nut on the backside or is it threaded into the genny body??

Does it look like the gasket material between the carb and the genny look to be paper gasket or does it look like RTV silicone? If RTV was used, there maybe some on the threads.

Couple things I have had good luck with. 1st, use some really good penetration oil and let it sit for a few days if you can, to let it creep in. WD40 is not a good penetration oil. 2nd, this seems wrong, but go back and forth between tightening and loosening the bolt/nut. 3rd, use an impact driver. 4th, use heat. A torch could damage any plastic parts in the area.
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Old 04-06-2021, 10:29 AM   #6
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Exactly what we needed and thank you! Will pm you about the carb offer.
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Old 04-06-2021, 12:06 PM   #7
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I'm a little confused about your post but here goes. On the Onan unit the 10mm bolts thread into the cast aluminum intake manifold. The bolts are steel the manifold is aluminum. Seizing leads to galling. The soak routine does work quite well, WD 40 is primarily a good starting fluid, penertrating fluid not so much. I use PD Blaster or if it's a bigger job a 50/50 blend of ATF and kerosene. Heat doesn't help much unless a the problem is rust. The heat expands the female part enough to break loose the rust. I've only used a whacker when what ever I was whacking was strong enough to be whacked.

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Old 04-06-2021, 02:53 PM   #8
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If you have already pulled the carb never mind, but many times SeaFoam Fogger will clear a varnished carb enough to get it running longer than just a few seconds. Then a good dose of SeaFoam in the gas will clear the varnish.
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Old 04-06-2021, 05:09 PM   #9
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If you have already pulled the carb never mind, but many times SeaFoam Fogger will clear a varnished carb enough to get it running longer than just a few seconds. Then a good dose of SeaFoam in the gas will clear the varnish.
Haven't pulled it yet so we'll try that first. Thanks!
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Old 04-06-2021, 05:15 PM   #10
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Haven't pulled it yet so we'll try that first. Thanks!

I don't know where you are located but I am sure from the name it is nowhere near Phoenix or I would give you a can of fogger that is sitting on my shelf in the garage
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Old 04-06-2021, 08:08 PM   #11
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I don't know where you are located but I am sure from the name it is nowhere near Phoenix or I would give you a can of fogger that is sitting on my shelf in the garage
LOL! Nope...Oregon. But appreciate the offer!
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Old 04-07-2021, 08:54 PM   #12
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Recently Replaced Onan Carb

Don't know the year/make/model of your rig so maybe this doesn't apply to you but others may find it useful.

I recently had my carb replaced on my 2019 Greyhawk Prestige 29MVP. The Onan has a 3 year warranty so I took it to the Cummins Service Center and they replaced it for FREE under warranty.

According to the Cummins guy they had to remove the entire generator to replace the carb which meant removing wiring and fuel lines. I'm a handy guy but not a professional mechanic so I won't mess with things that can cause a fire which easily results in a total loss of vehicle, injury or death. You might want a professional to do the work.

Another thing the Cummins guy told me is the Onan carbs fail because of ethanol in the fuel. The Ford engines can handle ethanol fine but generators don't do well with ethanol especially when they sit.

He told me to use ethanol free fuel when possible; costs about 10 cents more/gallon. It's easy to find here in Florida because that's what we put in our boats but not so easy to find elsewhere. He said use a fuel stabilizer that treats ethanol. I use the yellow STA-BIL. STA-BIL 360 Protection Ethanol Treatment And Fuel Stabilizer. Cummins guy said add fuel stabilizer to fuel tank then run generator for a while to pull the stabilizer into the generator's fuel system. I fill the tank full, add stabilizer then run the generator while driving to place I store it.

Sorry if this was off topic from your original post but I think others may benefit from this.
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Old 04-07-2021, 09:45 PM   #13
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Originally Posted by GoGator View Post
Don't know the year/make/model of your rig so maybe this doesn't apply to you but others may find it useful.

I recently had my carb replaced on my 2019 Greyhawk Prestige 29MVP. The Onan has a 3 year warranty so I took it to the Cummins Service Center and they replaced it for FREE under warranty.

According to the Cummins guy they had to remove the entire generator to replace the carb which meant removing wiring and fuel lines. I'm a handy guy but not a professional mechanic so I won't mess with things that can cause a fire which easily results in a total loss of vehicle, injury or death. You might want a professional to do the work.

Another thing the Cummins guy told me is the Onan carbs fail because of ethanol in the fuel. The Ford engines can handle ethanol fine but generators don't do well with ethanol especially when they sit.

He told me to use ethanol free fuel when possible; costs about 10 cents more/gallon. It's easy to find here in Florida because that's what we put in our boats but not so easy to find elsewhere. He said use a fuel stabilizer that treats ethanol. I use the yellow STA-BIL. STA-BIL 360 Protection Ethanol Treatment And Fuel Stabilizer. Cummins guy said add fuel stabilizer to fuel tank then run generator for a while to pull the stabilizer into the generator's fuel system. I fill the tank full, add stabilizer then run the generator while driving to place I store it.

Sorry if this was off topic from your original post but I think others may benefit from this.
Not off topic at all since that is exactly what we are thinking has caused the problem and I'm glad if someone else can learn from it too. We haven't had the rv long and of course have no idea what the original owner used as far as gas or additives. Appreciate your reply it verifies what we've been thinking.
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