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Open Roads Forum  >  Tech Issues

 > Onan Generator Hunts Under Load

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WingsFan1313

Pahrump, NV

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Posted: 06/12/20 02:20pm Link  |  Quote  |  Print  |  Notify Moderator

Hey folks! I wanted to first offer my thanks for those of you who answered my previous post. For those of you who don't know the backstory, I bought my first motorhome (2002 Fleetwood Tioga 24d) last month. As I am not very mechanically inclined, your help has been instrumental in my getting this far; when I brought it home, the generator would not start at all and you folks got me through that, so I thank you!

Here's where I'm at now, and it has a couple of us puzzled, so I figured I would reach out to you. I'll list all the known scenarios below. The generator is an Onan 4000 Microlite KY series.

- When I run the generator with no load, on first start-up, it runs well for 15 minutes or so. Voltage tests out within spec (127 +/- 4.5). After 15 minutes with no load, it starts to sag a bit (120-125 volts).

- The generator hunts with a heavy load on it (A/C or Microwave). This happens within 2 seconds of my turning either of those items on.

- If the generator starts to hunt, and I turn off the A/C or microwave, the generator continues to hunt -- it does not go back to normal no-load operation.

- If I turn the generator off and immediately back on, 7 times out of 10, it will come back to normal no-load operation. The other 3 times, it will continue to hunt.

- I ran Seafoam/Gas mix through the generator today to clean out all the valves, nooks, and crannies. While hooked up to the external can, the generator ran with no noticeable drops with no-load (I didn't try to put a load on it while running the cleaning). It was probably the best it ever sounded. When I hooked it up to main gas, it ran as above -- well for about 5 minutes and then I could hear the tone of the generator come down a bit.

Things I have done/tried (in this order):

- Filled the main gas tank with fresh gas.
- Checked the genset engine oil
- Replaced carburetor (got the generator running -- originally wouldn't start)
- Replaced fuel filter
- Replaced air filter
- Replaced spark plug
- Ran a hose to a can of Seafoam and gasoline to clean system
- Replaced fuel line from onboard gas tank to fuel filter

I also looked into the governor issue that many people have been talking about and downloaded the service manual to properly adjust it (within my limits -- I don't have a load bank to adequately test it). The issue is -- I can't get the generator to *not* hunt long enough to make adjustments to the sensitivity screw, and once it starts hunting, no manual adjustments bring it back to normal.

I'm stumped. Any help would be greatly appreciated. Thank you in advance! [emoticon]

* This post was edited 06/12/20 02:27pm by WingsFan1313 *

DownTheAvenue

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Posted: 06/12/20 02:45pm Link  |  Quote  |  Print  |  Notify Moderator

Since it apparently runs good when connected the external fuel supply, I would look towards the on board fuel source. Perhaps stale gas, even though you added new gas that may not be enough. Maybe a fuel pressure issue with the on board supple. I think the intank pump serves both the generator and the vehicle, and if I am correct, perhaps it is weak.

STBRetired

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Posted: 06/12/20 03:17pm Link  |  Quote  |  Print  |  Notify Moderator

There are separate fuel pumps. The vehicle and the generator each have their own. If you suspect a fuel issue, try running with a load when using the external fuel can. I don't think the fuel is at fault. When you replaced the carburetor, did you make sure the linkages and springs all ended up in the correct holes? I seems like the governor is making too big of an adjustment and once it starts oscillating it can't stop. Try turning the sensitivity down before the next load test.


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lightfoot

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Posted: 06/12/20 03:39pm Link  |  Quote  |  Print  |  Notify Moderator

If the gen runs normally when not connected to the onboard fuel tank, I bet there is a problem with the vent on the onboard tank. try removing the fuel cap and see what happens. that seems to be the only thing you have not tried.

dedmiston

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Posted: 06/12/20 03:43pm Link  |  Quote  |  Print  |  Notify Moderator

lightfoot wrote:

If the gen runs normally when not connected to the onboard fuel tank, I bet there is a problem with the vent on the onboard tank. try removing the fuel cap and see what happens. that seems to be the only thing you have not tried.


I was going to say the same thing. Is it possible that it's starving? Crack your fuel cap and see if the fuel flows more freely.


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WingsFan1313

Pahrump, NV

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Posted: 06/12/20 05:04pm Link  |  Quote  |  Print  |  Notify Moderator

Thank you for all of your replies -- the wind died down so I went outside and disconnected the main fuel tank to run it with the external can (with the Seafoam still in it). I let it run for a few minutes and then tried the A/C. It immediately started hunting again, so I think we can rule out stale gas in the main tank.

So while the AC was running and the generator was hunting, I tried turning the sensitivity down... literally all the way until the screw wouldn't turn anymore. The good news is that the hunting slowed... to the point where the A/C didn't panic and shut down. The bad news is that it still hunts... and now it seems to hunt on no-load start-up.

As I said, I am not very mechanically inclined, so trying to read the service manual to adjust the governor doesn't seem to help me figure it out. As I understand it, there are two screws that I need to worry about -- the speed adjustment screw (to dial in a no-load voltage within tolerance) and then the sensitivity screw on the governor arm (to dial in the correct frequency/voltage with a load on it). Maybe someone on here can explain it better than I can understand it through the manuals? Or maybe someone knows of a video on how to adjust these properly? I have scoured the internet and can't find a tutorial on how to adjust these correctly.

Thanks for your help! [emoticon]

Kpackpackkelley

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Posted: 06/13/20 08:16am Link  |  Quote  |  Print  |  Notify Moderator

Do you have the service manual ? Those choke rods come loose pretty easy so it will make it run rich. What does the spark plug look like ?

Lynnmor

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Posted: 06/13/20 08:37am Link  |  Quote  |  Print  |  Notify Moderator

Apparently it never ran for you on the original carburetor so you replaced it with what? I suggest that you disassemble the current, or both, carburetors and clean them properly. You could have introduced dirt into the current carburetor at installation. And please toss the snake oil and use only gasoline.





WingsFan1313

Pahrump, NV

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Posted: 06/13/20 04:38pm Link  |  Quote  |  Print  |  Notify Moderator

Kpackpackkelley wrote:

Do you have the service manual ? Those choke rods come loose pretty easy so it will make it run rich. What does the spark plug look like ?


Yes. I have the service manual. I will look into the choke rods to see if they are loose. Also the spark plug is a Cummins 1670275 Onan Spark Plug (found here.)

Kpackpackkelley

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Posted: 06/14/20 06:16am Link  |  Quote  |  Print  |  Notify Moderator

Need to know the color of the plug to see if it’s fouling. Wish I was closer it’s to hard trying to help over the net.

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