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Old 02-15-2021, 03:56 PM   #1
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Onan generator and surging

Okay I've Read in a million places about surging and the bottom line that I came up with was you can turn all the screws you want but the end result is replace to carburetor. So that's what I did. It does run a lot better as the old carb had all kinds of issues .

I have and Onan Emerald 3 6500. I've tried doing all kinds of adjustments and it just won't stop surging the only thing that stops IT from surging is turning idle up to hold it still. But this usually results in too highRPMs which creates too many volts. Sometimes when I start it start right up but it immediately starts surging, I can grab the throttle and stop it from surging and it'll stop it'll settle down for a minute and stay still but then it'll start bouncing around again. When I put on the new carburetor I didn't touch it I left it set exactly how came. I've since messed with it trying to get it to run right. The air mixture screw doesn't seem to have much effect, on the previous one by turn it in to far it starts stalling out so I started that point then back it up a little bit. But this one doesn't really seem to do that.
turning the idle up enough to get it to stop but turn the idle up enough to get it to stop but then runs fine it's just running a little too fast.
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Old 02-15-2021, 07:29 PM   #2
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I kind of need to do something about this myself. But beyond exercising mine I've only truly used it once for a few hours during a power outage.

I tweaked the adjustment on my governor linkage on my 6500 which seemed to help some. While fumbling with that I noticed that if I added a little resistance to the movement of that governor rod it smoothed out nicely. After a little experimentation I found a loosely wadded up paper towel between the rod and fan shroud modulated the surging very nicely under load. I know it's wrong and all but it works surprisingly well. At least as long as it's under load. Doesn't seem to work unloaded.

I look forward to suggestions of better ways to deal with the issue. I haven't tried another carb, but I have cleaned and tweaked my existing as much as possible.
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Old 02-16-2021, 05:48 AM   #3
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When mine (a '76 5K BGA) starts to surge I remove and clean out the carb to remove the white flocculent stuff that likes to partly clog the jets, and then adjust the mix for outside temperature. That has always, so far, straightened things out for a year or two as long as I run it once a month or so under load.

This problem started when our gas mix was changed from using MTBE to just ethanol additives for pollution control. (There is no good local source for undiluted gasoline.) The aluminum alloy they used in the 70's and ethanol don't seem to get along very well. I could soak the carb body in a strong lye solution to clean it, remove all the paint and varnish, and anodize it, I guess, but I'm too lazy.

A new replacement carb made of the same materials would seem likely to have the same problem.
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Old 02-16-2021, 12:37 PM   #4
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During the '80's and '90's I used to pick up extra money refurbishing carburetors on motorcycles (mostly) and ATVs and such that had clogged up due to being left to sit for too long. Outside my day job. I like to think I can clean and tune an old Onan carb but it still may be that I have missed something. Maybe.
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Old 02-16-2021, 02:47 PM   #5
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Just to throw it out there:


I had a surging issue on my Emerald when I first got it. On someone's recommendation, I replaced the spring holding the governor arm back and it cured it. Weakened, I guess, so the blowing from the flywheel vanes was having too much effect.
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Old 02-16-2021, 03:32 PM   #6
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Onan

Clean the carburetor and fuel system. Get a gasket kit before you do this.

Add Seafoam to gasoline as specified on container, it will help to prevent carb. problems. Seafoam has been used on outboard engines for decades.

The carb. has no air adjustment screw. You are referring to the idle fuel screw that lets fuel bypass the butterfly valve. This lets fuel into the venturi so the engine will run while idling. The only thing that controls the air is the throttle butterfly valve. *and of course the choke)
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Old 02-16-2021, 06:00 PM   #7
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This sounds more like hunting than surging. Need to adjust your speed (hZ} and governor sensitivity.

That the generator runs smooth when you hold the throttle tells me itís governor.

Get the manual and follow procedure for governor adjustment
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Old 02-16-2021, 07:23 PM   #8
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Quote:
Originally Posted by Bobby F View Post
I replaced the spring holding the governor arm back and it cured it.
Kind of been suspicious of that spring on mine since I spent a chunk of money with Flight Systems and got the thing functioning last year. After (I'm told) over ten years of non-functionality.

I bet such a spring is probably pretty cheap, right?
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Old 02-16-2021, 09:19 PM   #9
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Originally Posted by ROUGHRIDER3 View Post
Clean the carburetor and fuel system. Get a gasket kit before you do this.

Add Seafoam to gasoline as specified on container, it will help to prevent carb. problems. Seafoam has been used on outboard engines for decades.

The carb. has no air adjustment screw. You are referring to the idle fuel screw that lets fuel bypass the butterfly valve. This lets fuel into the venturi so the engine will run while idling. The only thing that controls the air is the throttle butterfly valve. *and of course the choke)
The carb is brand new it doesn't need cleaning, I put seafoam in a can of fresh gas and ran it for 4 hours. And it does have a "mixture" screw that alters the air/fuel mixture. and it's not an idle screw the amount of fuel is directly proportional to how open the butterfly is which means it's not an idle screw otherwise it would only affect an idle and it affects how it runs past Idle that's how a main Jet Works. more air more fuel. air mixture fuel mixture call it what you want it still adjusts the amount of fuel that mixes with the air. Standard operating procedure for naturally aspirated carburetors. it's also the reason that jet sits in the middle of the fuel bowl where all the fuel is. and they also don't sell gasket kits for these carburetors they are not rebuildable.
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Old 02-16-2021, 09:23 PM   #10
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Originally Posted by Corc View Post
This sounds more like hunting than surging. Need to adjust your speed (hZ} and governor sensitivity.

That the generator runs smooth when you hold the throttle tells me itís governor.

Get the manual and follow procedure for governor adjustment
I think it's the governor also and it will speed it up and slow it down but it still doesn't change the fact that I need to turn the idle up to her to hold it still. If it has any gap between the idle screw on a little plate on the throttle it'll start bouncing.
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Old 02-16-2021, 09:25 PM   #11
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Quote:
Originally Posted by Bobby F View Post
Just to throw it out there:


I had a surging issue on my Emerald when I first got it. On someone's recommendation, I replaced the spring holding the governor arm back and it cured it. Weakened, I guess, so the blowing from the flywheel vanes was having too much effect.
I had this thought because higher low and still the Hunts and surges. And if the spring was Stronger it would hold it still.
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Old 02-17-2021, 12:46 AM   #12
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Quote:
Originally Posted by GypsyR View Post
I bet such a spring is probably pretty cheap, right?
Very. $8, IIRC.
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Old 02-17-2021, 02:43 AM   #13
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The most common cause of surging is a LEAN condition caused by INTERMITTENT/ FAILING FUEL PUMP. The surge comes as fuel level in the float bowl falls to a critical level and engine starts to slow down, (fuel level rises, slightly) causing throttle to open, causing surge RPM increase, but subsequent fuel level DROP again in float bowl, REPEAT= Surge.
With GEN UNDER (1/2- full) Load and higher fuel use, it will DIE.. ORDER AND REPLACE FUEL PUMP AND FUEL FILTER check filter while apart and if clear, put New (or old) filter into spare parts for future. Filter is possible, but less likely, as GEN fuel pickup NOT in bottom of tank= NO/little water, and no tank bottoms trash. My riding mower demonstrates this same symptom every time I close fuel valve to store, and it surges before dying. PUMP fixed MY 20-yo Emerald Plus. ($30+/- Amazon) LUCK
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Old 02-17-2021, 08:54 AM   #14
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The pump is a thought but mine is new as that was the second thing I found to be wrong with my generator when I first set about bringing it back from the dead. The first thing was a cruddy positive battery cable connection.
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