Onan 5500 in our Class A had run quite well last fall on our way down to Florida. Since arriving and storing the unit it has run well, when it gets used (about every two weeks to keep it fresh), but It does sit more than normal. Earlier this week I was running it and after starting and running for a few minutes it started to surge. I was running a fairly light load (a heater) but it surged regardless of whether I ran the heater or not.I pulled the air cleaner while it was running and played with the choke plate. When fully open it surges but when I close the choke (partially or almost full) it runs much better. Is it running lean? What should I check or do before getting too deep into this?Thanks gang.

mikemc53 wrote:I pulled the air cleaner while it was running and played with the choke plate. When fully open it surges but when I close the choke (partially or almost full) it runs much better. Is it running lean?This is a classic problem of any carbureted small engine !Yes, it is running lean. It is highly like that the primary (low speed/idle) jet is blocked. It got blocked by some kind of "dirt"/foreign matter in the gas tank. Common when fuel (E10 or E00) sit in the tank for an extended period of time.What most people do not understand about small engine carburetors is that the "idle" jut is the PRIMARY jet. Fuel need to flow through it ALL OF THE TIME !I have had very poor luck try to clean primary jets with fuel additives. Usually this calls for removing the carburetor, disassembling, and soaking in solvent for several hours/overnight. For good measure, all passageways need to be probed with a stiff wire to make sure they are open. (Do not soak gaskets or rubber O-rings in solvent. It will destroy the gaskets and the O-rings will swell make re-assembly very difficult.Expect to pay $200 and up for this service ! Not difficult, just time consuming.

mikemc53 wrote: When fully open it surges but when I close the choke (partially or almost full) it runs much better. Is it running lean? What should I check or do before getting too deep into this?Most likely there is dirt, gum or other debris in the carburetor. First look for a bad vacuum hose or other air leak. Some use snake oil like Seafoam, and that might help, but you may need to disassemble the carburetor and do a proper cleaning.

Depending on your model, a new carburetor may cost ~$60. Replace if you are not comfortable cleaning it.

I had a surging problem with my Onan 5000. I removed the air cleaner and used a spray can of Seafoam, I sprayed it into the carburetor intake until it almost stalled. Then I left it idle a few seconds,and sprayed again. I did that several times and finally sprayed the Seafoam until the generator stalled.I left it sit several hours (actually overnight).When I started the generator it ran smooth and continues to run smooth.Its worth trying and is easier than cleaning/replacing the carburetor.Sometimes Snake Oil works.. :)

2112 wrote:Depending on your model, a new carburetor may cost ~$60. Replace if you are not comfortable cleaning it.+1 for a NEW replacement.

generator surge | Good Sam Community

bobsallyh
Explorer II
Dec 23, 2019
tiffy2000, I feel your pain. Last carb for our Marquis Gold 7000 was 192.00 thru an independent Onan repair shop. Now due for another. Like you said, no knock off available and not rebuildable, just another throw away item. Nothing PO's me more than when people fire up Yamahazees and Hondas, off they go, no choking, no puking, I'm sure you know the routine only too well also.
Bobbo
Explorer II
Dec 23, 2019
theoldwizard1 wrote:
gbopp wrote:
When I started the generator it ran smooth and continues to run smooth.

Its worth trying and is easier than cleaning/replacing the carburetor.

Sometimes Snake Oil works.. :)

Sometimes ! I have never been that lucky !!

I HAVE been that lucky. I had a riding mower with the carb so gummed up I had to use starter fluid (ether) sprayed directly into the air intake to start it. Even then, it ran rough. I used double strength Seafoam for a season. By the end of the season, the mower ran like it had a new carb installed.

I like the suggestion about the spray Seafoam into the air intake. But, I would also ALWAYS have Seafoam in its fuel. Actually, since that episode I DO always have Seafoam in the fuel for mine.
garyemunson
Explorer II
Dec 23, 2019
Best cure is not let gas get stale. Seafoam or any other stabilzer will only do so much. If you have 60 gallons plus of stale gas you will have problems. The more you use your RV, the better.
Dave_H_M
Explorer II
Dec 22, 2019
give it a triple strength shot of seafoam. Who knows, maybe it will be your day.
gbopp
Explorer
Dec 22, 2019
theoldwizard1 wrote:
gbopp wrote:
When I started the generator it ran smooth and continues to run smooth.

Its worth trying and is easier than cleaning/replacing the carburetor.

Sometimes Snake Oil works.. :)

Sometimes ! I have never been that lucky !!

Maybe that explains why I never won the lottery (except the one in Nigeria).
I wasted all my luck on snake oil.
tiffy2000
Explorer
Dec 22, 2019
I have a Onan 5500 and have the same issue. Two years ago I had a surging issue and replaced the electric fuel pump (after replacing the fuel filter) . That appeared to fix it until this year, replaced filter, ran SeaFoam through it , no better. Took off carb bowl with carb in place, cleaned it as good as I could...also noticed governor linkage had popped off governor and popped that back on.... purred like a kitten with / without load. Vacation , started surging again.... probably will end up forking out the $315 for a new carb even though it irritates me as I bought a new carb for my Champion for $25....can't find a knock off for this 5500 Onan
theoldwizard1
Explorer II
Dec 22, 2019
rrupert wrote:
Small engines and E10 gasoline are a bad combination. Run non-ethanol gas if you can. Fuel stabilizer also is a good idea especially if the engine sits with fuel between uses.

IMHO people make to big of a deal about E10 in small engines. All of mine run E10 (E00 is very difficult/expensive in my area) and most will sit all winter/summer without stabilizer. I do like to drain the carburetor at the end of the season which usually means the equipment need a shot of something to start up next year, but that is a one time thing.

The biggest problem I run into is equipment with large tanks (portable generator) that do not get used a lot. If your equipment does not use more than 2 or 3 tanks per season, you should drain the tank completely once a year.
js218
Explorer
Dec 22, 2019
^^^One of my hobbies is large scale gas cars and buggies constantly modified the 2 stroke engines also 2 of my atvs are vintage 2 stroke Suzuki Quadzillas, so the ultrasonic cleaner gets a work out.
theoldwizard1
Explorer II
Dec 22, 2019
js218 wrote:
I use a ultrasonic cleaner for all my carb cleanings, atv, sleds, lawn equipment, snowblowers ect.

A heated ultrasonic cleaner is by far the best solution. I like to putter around with small engines and I still have not been able to convince myself to make the investment.
theoldwizard1
Explorer II
Dec 22, 2019
gbopp wrote:
When I started the generator it ran smooth and continues to run smooth.

Its worth trying and is easier than cleaning/replacing the carburetor.

Sometimes Snake Oil works.. :)

Sometimes ! I have never been that lucky !!

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