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Old 06-13-2018, 03:07 AM   #1
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Brand: Thor Motor Coach
Model: Vegas 25.2
State: Missouri
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VEGAS ONAN 4000 Generator starting issues

Our coach is right at two years old. We have started the generator every month to month and a half (and ran it under load) and never had any issues with it.

Last started it in April (started right off), then in May had trouble starting. Worked with it and tried longer prime time (30 seconds) and the generator fired right up.

Now, it will not start. It will crank, but never fire. If we use starter fluid, the generator will fire right up and run for an hour (until I stop it) Running smooth and sounding great. It just will not start.

Replaced spark plug, switched to a gas can with fresh gas (gas in RV tank had been treated) Gas in RV tank looks and smells good, but even on new gas supply, the generator will not fire.

Has anyone had anything similar? If so, what was your solution?

Up for any ideas. Thinking of mixing up some seafoam and gas in a small tank and running in through and letting it set for a couple of days.

Been working on this for a couple of weeks and frustration level is starting to rise (along with the summer temps here in MO)
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Old 06-13-2018, 03:24 AM   #2
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State: Florida
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Replace the fuel filter. Is the fuel pump working? Gas in the bowl? I understand there have been issues with the fuel pumps.
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Old 06-13-2018, 03:41 AM   #3
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Originally Posted by Tfryman View Post
Replace the fuel filter. Is the fuel pump working? Gas in the bowl? I understand there have been issues with the fuel pumps.
I hadn't replaced the fuel filter yet (since it runs GREAT, just wont start) But I will try that...
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Old 06-13-2018, 03:43 AM   #4
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Sea Foam fixed ours, it would die under a heavy load.

Here's a quote from a very good thread on RV.NET.

RV.Net Open Roads Forum: How to change carburetor on Onan generator 5500

"Onan does NOT supply carb rebuild kits due to all Onan carbs are built for California emissions, which require a tamperproof carb
That said, you CAN clean out the carb and it is easy. On the bottom of the carb is the fuel bowl and you will see a plastic housing around the bowl screw that allows you to turn it 1/2 way. Gently cut that plastic housing OFF and then you will be able to unscrew the bowl and then drop it out. You will see all the gunk in the bowl. IF you understand small carbs you will know where the needle jet is, it unscrews( very small slot screwdriver) and you will find 4 rows of 4 microsmall pin holes. Those small holes are what are clogged up. You then use carb spray and compressed air and clean/blow out the jet holes, clean out the bowl and clean out the float/needle for the float with carb cleaner. The gasket/o rings will not get damaged from this so you can reuse them. Doug "

Hope this helps
a can of sea foam and a gal of gas first, then clean the carb,...then $$$ for a new carb.
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Old 06-13-2018, 01:07 PM   #5
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Model: Four Winds
State: Michigan
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Originally Posted by abjbrtd View Post
Sea Foam fixed ours, it would die under a heavy load.



Here's a quote from a very good thread on RV.NET.



RV.Net Open Roads Forum: How to change carburetor on Onan generator 5500



"Onan does NOT supply carb rebuild kits due to all Onan carbs are built for California emissions, which require a tamperproof carb

That said, you CAN clean out the carb and it is easy. On the bottom of the carb is the fuel bowl and you will see a plastic housing around the bowl screw that allows you to turn it 1/2 way. Gently cut that plastic housing OFF and then you will be able to unscrew the bowl and then drop it out. You will see all the gunk in the bowl. IF you understand small carbs you will know where the needle jet is, it unscrews( very small slot screwdriver) and you will find 4 rows of 4 microsmall pin holes. Those small holes are what are clogged up. You then use carb spray and compressed air and clean/blow out the jet holes, clean out the bowl and clean out the float/needle for the float with carb cleaner. The gasket/o rings will not get damaged from this so you can reuse them. Doug "



Hope this helps

a can of sea foam and a gal of gas first, then clean the carb,...then $$$ for a new carb.


I ran across a similar problem last winter while we where in Florida, the problem was on the neighbors 2016 class A. The short story is their generator wouldn't run if there wasn't at least a 1/2 tank of fuel in the RV. We assumed this was a safety thing preventing people from being stranded because they run out fuel due to running the generator while camping.
Hope this is you problem
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Old 06-13-2018, 01:33 PM   #6
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Not enough fuel in the tank for the generator to run... that would sure be the easiest one to fix! I also hope that this is the problem.
But I'd also be checking the fuel pump..
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Old 06-13-2018, 04:09 PM   #7
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Model: 2013 31L
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do you know how to check for the error code? the flashing light?

I've never personally seen a code flash that was helpful the times I've had generator issues, but maybe that could help you clue into what it is.... maybe.

I've this a lot, that the pumps are often an issue with these things...but it doesn't make sense to me that the thing runs but won't start. I think if it was filter or pump it would struggle when running.
the filter, especially, but also a weak pump would cause problems when it's running under load (flow rate is higher)

I'm leaning to a carburetor issue. One of the jets maybe plugged up a bit.... like an idle jet? maybe the sea foam trick would work???

Not saying that this would help your issue....Once, my generator started surging. I found that if I turned the altitude screw full way, I think to the high altitude direction, it would smooth out. I turned that thing back and forth a few times while it was running, might have let it run a bit while it was in a smooth adjustment, and then corrected for the right altitude and the thing has ran smoothly ever since...
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