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Old 02-15-2015, 06:44 PM   #1
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Onan 4000k Generator surging voltage

I have an Onan 4000 generator in my Sunseeker RV. The generator starts fine and runs...however, it seems to be surging and the voltage inside swings from around 100 volts to 120 volts. However, if I turn on the AC and put it under a load the surge diminishes....until the AC cycles off and then you can hear the surging again. I am concerned that the voltage shift might damage the AC or other electronics. Any thoughts?
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Old 02-15-2015, 07:41 PM   #2
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my first thought, as ive seen this kind of thing before is a dirty carb on the genset. under light load the 'low speed' jet being partially plugged causes a lean out which causes the engine speed to surge (albeit it can be hardly audible, a laser/photo tach is nice). when the generator is under load, the throttle opens and the effect of the partially plugged low speed jet is negated as it has little influence at that point.

Short of this, if the generator is running 100% with no engine surging, the AVR could be on its way out the door.
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Old 02-15-2015, 07:53 PM   #3
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Quote:
Originally Posted by rgarner View Post
I have an Onan 4000 generator in my Sunseeker RV. The generator starts fine and runs...however, it seems to be surging and the voltage inside swings from around 100 volts to 120 volts. However, if I turn on the AC and put it under a load the surge diminishes....until the AC cycles off and then you can hear the surging again. I am concerned that the voltage shift might damage the AC or other electronics. Any thoughts?
Agree with Dave and you. Additionally if governor is bad the speed will surge and voltage with it. Fuel strainer may be clogged but not likely. Even carb may not be a problem unless its sit around for long periods with old fuel. My guess take it to an Onan dealer or equiv. That voltage swing is not good for motors or electronics.
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Old 02-15-2015, 08:29 PM   #4
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I just helped my neighbor with his doing the exact same thing. He had forgot to run his after adding Stabel to the gas. The FW sat from April until November. He was told by Cummins to replace the carb 250$. We ran Seafoam through it and that helped but ultimately we took the carb apart and cleaned everything. My belief is the slow jet was clogged as mentioned above. It runs like a top now. It a very simple carb.



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