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mikemc53

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Posted: 12/22/19 07:09am Link  |  Quote  |  Print  |  Notify Moderator

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.


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theoldwizard1

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Posted: 12/22/19 08:09am Link  |  Quote  |  Print  |  Notify Moderator

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.

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Posted: 12/22/19 08:12am Link  |  Quote  |  Print  |  Notify Moderator

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.





2112

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Posted: 12/22/19 08:25am Link  |  Quote  |  Print  |  Notify Moderator

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


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gbopp

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Posted: 12/22/19 10:44am Link  |  Quote  |  Print  |  Notify Moderator

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.. [emoticon]

time2roll

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Posted: 12/22/19 11:06am Link  |  Quote  |  Print  |  Notify Moderator

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.


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js218

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Posted: 12/22/19 11:44am Link  |  Quote  |  Print  |  Notify Moderator

I use a ultrasonic cleaner for all my carb cleanings, atv, sleds, lawn equipment, snowblowers ect.


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rrupert

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Posted: 12/22/19 12:20pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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theoldwizard1

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Posted: 12/22/19 02:20pm Link  |  Quote  |  Print  |  Notify Moderator

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.. [emoticon]

Sometimes ! I have never been that lucky !!

theoldwizard1

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Posted: 12/22/19 02:22pm Link  |  Quote  |  Print  |  Notify Moderator

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.

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