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Old 03-21-2012, 05:26 PM   #1
Join Date: Nov 2011
Location: Phoenix, AZ
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Onan Carburetor Plugged

I have an Onan Marquis Platenum 5500 gas generator on my Motorhome. If I dont start and run the generator for an hour or 2 ever couple of weeks it gums up the Carburetor and the dealer repair center has to put a new one it for a bunch of bucks.

I have heard that this is a problem with Onan gererators. I thought about gas treatment but for 80 gallons of gas that would require a bunch of treatment.

Has anyone put a gas shut off valve in line and let the generator run out of gas after shutting off. This works on some of my big honda spray engines it will probably work on this.

Appreciate any help


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Old 03-21-2012, 05:42 PM   #2
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Gary, someone is sh------g you up. I have 506 hours on my Onan, but it may need something. Oil changes with filter is all I do. Why dont you have to change anything on your engine? I do run mine for 20 min. once a month if it is not on the road, with a load on it for the windings. F9ind another mechanic.

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Old 03-21-2012, 05:51 PM   #3
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I had the oil changed and new filter put in but it still does not get gas. It was the carb, after the change it is fine. I have the old part.
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Old 03-21-2012, 05:59 PM   #4
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I run Seafoam treatment thru our V10 about every 6 months or so. Since the Onan runs off the same tank it gets a shot too. I use stable also. I had carb problems with the Onan because it set for a good while and I didn't run it like I should. I didn't have to replace anything just a PITA to get the float unstuck. Now I have a PM schedule that I do once a month.
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Old 03-21-2012, 06:30 PM   #5
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Before I started fulltiming I had problems with my Kohler genny and the gas going sour from sitting too long. When I got my MH the carb on the genny needed a rebuild since it had sat for 2 years without running. I rebuilt the carb and got it running but I was getting dirt from the tank.

What I did was install an inline fuel filter a few feet from the fuel pump. A few times a year, I take the fuel line off the filter and drop it into a one gallon gas can loaded with lots of Seafoam. I run the whole gallon of Seafoam heavy fuel and the generator runs great afterwards.

I have since cleaned the MH fuel tank.
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Old 03-21-2012, 07:03 PM   #6
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Hi Gary, I had the same problem with my ONAN generator and a shut off valve to run the carb dry solved the problem. I think humid climates contribute to this problem. Hope this helps narrow it down.
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Old 03-21-2012, 07:27 PM   #7
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Did you have any trouble priming it after it had run dry? I guess I can find a shutoff valve at one of auto parts or camper stores.
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Old 03-21-2012, 07:28 PM   #8
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Whoops forgot to thank you for responding
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Old 03-21-2012, 07:56 PM   #9
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I would like to help but I have a diesel and we have problems with algea if you don't run it enough
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Old 03-21-2012, 10:18 PM   #10
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Gary my 2003 Marquis Platinum was a fuel injected model. I was under the impression all Platinum models were EFI? Have you verified you have a carb.?

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Old 03-22-2012, 12:52 AM   #11
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Once a year I use 6 cans of Chevron fuel cleaner form Costco in my 75 gallon tank. While that mix is in there I run the generator for about an hour.

This last time I used 6 cans of Seafoam.

Yes it's expensive, however it does help because my Onan 5.5 runs great after 7 years.

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