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Old 12-08-2021, 03:23 AM   #1
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THOR #4687
Onan 4000 generator wont start

I have a onan generator on my 2016 Vegas that will not start. It will "almost" turn over with puffs of smoke and a chugging sound, but will not turn over and run. Have been starting the genny every two weeks and running 30-45 minutes under load. Changed spark plug (plug was covered with carbon), changed fuel filter, changed air filter, checked oil level.

Havent tried starting fluid and havent checked spark on plug(since it tries to start) Anyone have any ideas on this?

I had to replace carb two years ago and have been faithfully running it on the two-three week schedule on advice from Cummins when they replaced it. (bad gas)

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Old 12-08-2021, 03:35 AM   #2
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If the starter is rotating the generator, it is "turning over".

You have a generator that turns over but doesn't start.

How much gas is in the tank? The generator fuel pickup is above 1/4 tank.

When you prime it can you hear the fuel pump running?

Have you pulled the spark plug and checked it? Checked for spark?

Go ahead and try the starting fluid - it will give you more information in your troubleshooting.

There's no magic answers - you have to logically troubleshoot the no start issue.
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Old 12-08-2021, 03:43 AM   #3
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Just to clarify your terminology... if it "turns over", that means the engine is "cranking"... but not necessarily starting. If you had for instance, a dead battery - it wouldn't "turn over" (crank).

Anyway, my guess at this point is a carb problems OR bad gasoline (again), because it sounds like fuel problems. Stupid question (but must be asked): Are you certain the flow direction of the new fuel filter is correct?

I would suggest adding marine grade Stabil (blue, not red) to your gasoline tank AFTER you get everything squared away... and use a different gasoline brand/supplier.
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Old 12-08-2021, 03:54 AM   #4
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How much gas is in the tank? Full tank.

When you prime it can you hear the fuel pump running? Yes can hear it running and smell gas after priming.

Have you pulled the spark plug and checked it? Checked for spark? Plug looked covered in carbon. Haven't checked for spark yet, did replace plug.

Go ahead and try the starting fluid - it will give you more information in your troubleshooting. A little fun shy on this after hearing of someone catching their Genny and RV on fire doing that.

Yes, am afraid it might be carb again, but not sure how to prevent it, since was starting and running every two weeks, keeping full tank of gas. Use the STABIL RED ( never heard of STABIL BLUE) The last time Cummins charged 800 for carb replacement.

Didn't use as much last year due to COVID, but trying to prevent issues from lack of use.
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Old 12-08-2021, 05:32 AM   #5
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Stabil Marine 360. It's used in boats (marine). Look it up for info. The RED is for storage only, whereas the Marine 360 (blue) is used year round.

I also suggest trying the starting fluid. You shouldn't have a fire unless you're squirting half a can!

If it fires up and runs for a brief instant with the starting fluid, that's strong evidence you have a fuel problem... either bad fuel (ethanol/moisture contamination), or starvation - something obstructing the fuel flow.
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Old 12-08-2021, 11:37 AM   #6
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Did you use fuel stabilizer in the fuel tank?

I have to prime mine for a count 60. Then again for 15. Then it fires up. Been that way since new. Itís a long way from fuel tank to genny.

You say it chugs. Are your batteries fully charged?

Is oil low or overfilled?

I havenít used ether starting fluid since the Ď70s when my Doge Dart backfired thru the carb and took all my facial hair with it.
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Old 12-08-2021, 01:46 PM   #7
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Fuel pump checked? Best way is to use the start button at the genset and hit prime... you should be able to feel the fuel pressure in the hose at the carb.
These tend to be cheap units that will have problems. You didn't say if the fuel pump was replaced with the carb... should have been.
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Old 12-08-2021, 03:57 PM   #8
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Quote:
Originally Posted by Chateau_Nomad View Post

- Stupid question (but must be asked): Are you certain the flow direction of the new fuel filter is correct? -
You can't put the filter in an Onan 4000 genset in backward it threads into the unit.
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Old 12-08-2021, 04:08 PM   #9
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Originally Posted by MJC62 View Post
You can't put the filter in an Onan 4000 genset in backward it threads into the unit.
Check! That hasn't come up as a maintenance item on mine yet, so I hadn't checked it. Good to know... one less thing I can screw up!
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Old 12-09-2021, 11:04 PM   #10
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Generator problem solved!

I resorted to taking it to Cummins to check it out. Turned out it was the choke stuck causing the generator to flood...

Bad thing, since all the vehicles are injected now, my experience with carbs from my younger days seems to have faded somewhat. My traveling partner asked if I had checked the choke, but wasn't sure where to actually check it on the generator. A 290.00 lesson, but could have been worse, they said their price to replace the carb is now 1100.00.

I now know that the 294.00 replacement ONAN carb on Amazon will be the way I go if I need a carb in the future. It doesn't look to hard to replace (as I was crawling around in the air filter chamber)

Thanks for all the advice. Having an RV is definitely a "learning" (if not inexpensive) experience!

I wanted to post the solution, as I hate people who solve their issues and never share the "fix"
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Old 12-10-2021, 03:24 AM   #11
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Huh... a choke! Who woulda thunk that? I thought the primer took care of that...

Thanks for the valuable info!!
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Old 12-10-2021, 08:17 AM   #12
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Quote:
Originally Posted by Jimbo56 View Post
Did you use fuel stabilizer in the fuel tank?

I have to prime mine for a count 60. Then again for 15. Then it fires up. Been that way since new. Itís a long way from fuel tank to genny.

You say it chugs. Are your batteries fully charged?

Is oil low or overfilled?

I havenít used ether starting fluid since the Ď70s when my Doge Dart backfired thru the carb and took all my facial hair with it.
Yes, I had the same (if not as extreme) experience as you back in the 70's with a 73 camaro. And in this stage of my life, I value every strand of hair I can cultivate on my head (face or otherwise)
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Old 12-10-2021, 12:22 PM   #13
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Make sure when you do run the generator that you have it under a load (plug in a heater of some sorts) never run a generator without a load.

See page 2-5
https://www.cummins.com/sites/defaul.../0981-0159.pdf
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Old 12-15-2021, 10:08 PM   #14
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When I purchased my 2017 Vegas the Generator started and ran during the walk through inspection. When I tried to start it 2 weeks later it wouldn't start. I tried everything I could think of short of replacing that over priced carb and finally pulled the fuel line from the carb and put a separate fuel line on the carb and plugged the line from the tank. I attached a funnel to the hose, elevated it above the generator and filled with a large amount of Sea Foam and a smaller amount of Gas. When I started the generator it ran very rough for a few minutes gradually getting stronger and stronger until it was running well. I poured some more gas into the funnel and ran it for about 15 minutes. I have never had to do anything again other than running it once or twice a month under load. Very cheap fix and easy to do. I had cleaned and adjusted the linkage and everything else before trying that solution.


I used to store my ATV for the summer here in AZ when I would leave for higher elevations in the spring. I used Stabil the first summer and when I got back I could never get it to run right until I tried the sea foam, let it sit for over night and started it in the morning. It would only run with the choke on for about 10 minutes then cleared up and ran well for a few years before I sold it. I'm a firm believer in Sea Foam and not so much with the Stabil. (I have no commercial interest in Sea Foam)
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Old 12-16-2021, 02:05 AM   #15
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If it won’t turn over, it’s the battery. Does it make a clicking sound like the starter relay Is getting power.
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Old 12-16-2021, 02:08 AM   #16
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Originally Posted by Glensouth View Post
...... Does it make a clicking sound like the starter relay Is getting power.
Did you read the thread? Specifically post # 10?
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Old 12-16-2021, 05:26 PM   #17
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Very Informative Thanks

Thanks for posting the solution...
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