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Old 03-17-2019, 08:53 PM   #1
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Default Surging (?) Onan QG2800

I have an Onan gas 2800 generator purchased in mid 2017 that now has 44 hours on it. It's been run for a variety of times from a few minutes to hours, but less recently - only for exercise.

The last couple of times it has been run, it seems to be making a rhythmic noise that seems like the power is going up and down. Here is a video. It's under load (AC) and the sound oscillation doesn't seems to change even when the load is removed. Any ideas?

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Old 03-17-2019, 10:47 PM   #2
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I have an Onan gas 2800 generator purchased in mid 2017 that now has 44 hours on it. It's been run for a variety of times from a few minutes to hours, but less recently - only for exercise.

The last couple of times it has been run, it seems to be making a rhythmic noise that seems like the power is going up and down. Here is a video. It's under load (AC) and the sound oscillation doesn't seems to change even when the load is removed. Any ideas?

Yes "Surging", sounds classic.

The tiny little jets in the carb have varnish that has formed after the gas or gas/ethanol has dried up. Many use Seafoam in the gas to solve this IF not too bad. Or strong carb cleaner into the carb by disconnecting the carb fuel hose, access for the carb cleaner. Or replace the carb.

90% chance varnish, imo.

Most start with the Seafoam.

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Old 03-22-2019, 01:58 AM   #3
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Well, the update is that after about 4 hours using a gas/cleaner mix feeding directly into the Onan, most of the surging oscillation is gone. But it clearly likes to be under a heavy load. If we run everything there is to run, it doesn't surge, but if there's no load it will start to surge and will continue to do so indefinitely
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Old 03-22-2019, 02:48 PM   #4
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Disappointing, not good enough, sorry about that.

What did you use? What percentage....?

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Old 03-22-2019, 07:27 PM   #5
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Can you screw the float bowl off? By turning it, you can drop it down and after clening the bottom inside you may try again.. IF that doesnt work, you can even continue to remove the adjustable (high altitude/low altitude) adjustment. Do this by 'GENTLY' turning the set screw in and count the half (or quarter) revolutions until you hit bottom.. Write that down.
Then remove completely and clean the gunk out. clean thoroughly untill everything looks like new aluminum and brass. Put the adjustment screw/needle back in until bottoming out.. then back out again by the number of revolutions you had marked down. Assembly bowl and try to run again..

That did the trick for me. Good luck!
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Old 03-22-2019, 07:32 PM   #6
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Can you screw the float bowl off? By turning it, you can drop it down and after clening the bottom inside you may try again.. IF that doesnt work, you can even continue to remove the adjustable (high altitude/low altitude) adjustment. Do this by 'GENTLY' turning the set screw in and count the half (or quarter) revolutions until you hit bottom.. Write that down.
Then remove completely and clean the gunk out. clean thoroughly untill everything looks like new aluminum and brass. Put the adjustment screw/needle back in until bottoming out.. then back out again by the number of revolutions you had marked down. Assembly bowl and try to run again..

That did the trick for me. Good luck!
Onan changed the carb with the newer models? I did not know about removing the bowl?

And gunk? 44 hours?

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Old 03-22-2019, 07:48 PM   #7
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Onan changed the carb with the newer models? I did not know about removing the bowl?

And gunk? 44 hours?

Bud
Maybe the newer ones do not have the removable bowl.. mine is a 97 model.
I tried the seafoam too, but that varnish type of coating wouldnt dissappear even after running with seafoam for a while and letting it soak overnight.. Scrubbing with some cloth, was the only way to get that varnish off.
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Old 03-23-2019, 01:19 AM   #8
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And gunk? 44 hours?

Bud
Not how long it ran, but how long since it ran. Mine surges if it goes too long without running. But so far, its cleared itself after a half hour or so.
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Old 03-23-2019, 02:34 PM   #9
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Seafoam wasn't available locally so we used Chevron Techron as directed (I believe 1 oz/gallon but don't have the bottle handy).

And I have to correct my earlier post to say it was run 1.5 hours with this mixture going directly into the fuel line of the Onan.

The generator sat idle for nearly 4 months as we had a series of health issues this past winter. We know it needs to be exercised, just couldn't get there. Next winter we'll put some Sta-bil in the fuel before winter just in case.
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Old 03-23-2019, 03:25 PM   #10
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I have no idea if sta-bil will keep the fuel from drying out in the carb jets or not. If not, I also don't know if it will somehow keep the varnish from forming or not.

Some folks don't want to exercise the generator, so they have added a cutoff switch to the fuel line to run the engine out of fuel. The small Yamaha generator has that feature. Maybe Honda does also by now.

Just sitting with Seafoam in the fuel will assist some. In the worst cases folks have used Strong carb cleaner mixed with gas directly into the carb, start the engine and then kill it leaving the strong carb cleaner in the jets. Let it sit for awhile, then do it again start momentarily and kill the engine. There are discussions about potential carb damage, but if this is the only solution, why not. If it works, great, if not replace the carb.

I have only used Seafoam once with very mild surging for a few minutes about 8 years ago. I simply ended the trip with about 3/8 of a tank of fuel, added a full dose of Seafoam and ran the generator for a few minutes. I had little doubt it was the carb jets.

The generator is 14 years old, 12 with me. I exercise it for about 35 minutes every 35 days when not using the B. The generator/B is happy with me spending days in the B after 2 hurricanes with the generator running a Lot. The last hurricane forecast required no one do any preparations, 75 mph wind that would past right through the New Orleans area. That meant I only had about 3/8 of a tank, big problem. The 75-80 mph wind was correct, But lasted for days. When living in a city there is Lots of Rotor, so it is 75 mph this direction the opposite direction........... Took out most of the power with most folks without power for days Including Gas Stations with my gas! I could not siphon gas from my car. My neighbor was downtown in some fancy hotel with power. He had a full tank with his new truck. I was able to siphon his gas, victory which meant ac was available for a long time.

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