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Author Topic: Surging Onan 4000 microquiet  (Read 177 times)


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Surging Onan 4000 microquiet
« on: September 11, 2017, 08:39:39 PM »
Still no power after Irma...
started my generator today and it was surging fairly badly.  I used it on our trip a week ago and it ran fine till I was heading to the lot to store it it surged a bit, but nothing alarming.

Anyway....after a couple minutes of hoping it would calm down today, I opened up the cowling, I could see what I assume was the spring loaded governor rod actuating with the surges. If I held it the genny would nearly stall.

Last ditch grab for something to try, I adjusted the altitude adjustment screw to it's highest altitude setting.  Immediately it smoothed out.  I let it run there for about a minute then set it back down to sea level.  Ran smooth for several hours

odd right?  Oh well I'm not arguing with it..... but do you have any thoughts?
Brad (DW + 3 kids)
13 Thor Chateau 31L Class C on Ford E-450
'06 Silverado
'05 Rockwood Freedom 1910 (5-1/2 years)
former tent campers


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Re: Surging Onan 4000 microquiet
« Reply #1 on: September 12, 2017, 04:12:23 PM »
Surging on a carburetor engine usually indicates a rich fuel mix, ie, too much fuel going down the carb throat vs air. So, adjusting the mix screws can compensate by allowing more air to be delivered in the mix, improving the air/fuel ratio.   The root cause is almost always some restriction in air flow path or can be caused by fuel bypassing the fuel jets possibly due to the float needle seat not completely sealing and allowing the carb bowl to overflow into the carb throat (flooding). Severe flooding can't be compensated with air/fuel mix adjustments and the engine will choke out and die.
SO..... I would remove the air filter, start the engine and squirt some carb cleaner into the carb in small amounts, not enough to stall the engine, in case the butterfly is sticking.  Follow that with some SeaFoam. If the problem doesn't resolve, a carb cleaning or rebuild is suggested.
Just my 2 cents..  Good Luck.
2005 Forest River TT 27BHSS and 2009 Heartland Sundance 2998RB 5vr
2007 Chev Silverado 2500HD WT crew cab, LB, 6.6L, Allison 6sp, B&W Companion Hitch
Retired Biomedical Engineer

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