Onan Backfire - Not A Good Thing

[Makin__Do]

When not traveling I run my Onan 2800 for one hour under a 1500w load every other week. Always, when starting it takes a couple of tries for a few seconds for it to start, drawing up gas from the fuel tank I would assume. This past Friday I fired it up and after the second try the engine back fired. Pushed the start button again and it fired right up and ran smooth. Now, not being an expert, I would think that a back fire is not good for the engine. The temp outside was 37F and the fuel in the tank is about six weeks old and has Sta-bil added. The onan has 155 hrs on the meter. So, what might be the reason for the backfire?

[Makin__Do]

Thanks for the reply TEXAS. It's now easy to see where you are coming from. It is nice to know for now I don't need worry about a one time event, at least not let. I'm a firm believer in running an engine often and a fairly regular basis. Hate to put hours on the meter, but it's better than paying $700 plus to have it overhauled.

FWIW, GENSET 2.8KVFA26100K, serial A05074019.

[mkirsch]

That's it in a nutshell right there: Backfires are generally NOT harmful, and an isolated backfire is NOT necessarily an indication of some underlying issue.

If pieces didn't fly off and it ran fine afterwards, shrug your shoulders, make a mental note of it, and move on. In the spirit of the "my arm hurts" analogy, it's like going to the doctor and telling him you felt a brief twinge of pain in your arm two weeks ago.

[TEXAS]

Yes he has a 2800. But what spec what serial number.Things change and with each change you have a different spec letter.A change could be minor or major.Just saying I have a 2800 is like saying I have a Mustang.Ok but what year is it. You don't go to a doctor and just say my arm hurts. Which arm.

Hard to give advice when you are not sure what you are working on. This is why all the techs that know left this site.Got tired of trying to help without the proper information.

Makin Do Keep running your generator as you are. The worst thing you can do is let it sit. It doesn't care what the temp is run it. Helps keep things in shape. I have been in the generator business since 1968. Most of my calls were to gensets that were allowed to sit. By people thinking they were saving them.

I wouldn't worry about the backfire to much.If it runs fine after that. Many things can cause it.Sometimes it just happens.

[time2roll]

Deleted

[ernie1]

TEXAS:
Didn't the op say that he had an Onan 2800? I knew what it was and I have the same one. What are we missing here?

[Makin__Do]

TEXAS wrote:
Again someone asking for help. But no idea what they have.

Not quite sure what you mean. Could you please expand on your comment?

[Makin__Do]

Thanks for the replies. I'll wait until I fire it up again to see if the backfire happens again.

Sam, I run a 1500 watt heater for my load after the engine warms for a few minutes. Here in North Central WV I think I'll have wait more than a few weeks for a warm spell, Canada is sending us some real cold weather at present. Running the generator every two weeks is not inconvenient for me since I walk past the rig at least six times a day. Always enjoy sitting inside for awhile.

[TEXAS]

Again someone asking for help. But no idea what they have. This is why all the generator techs left the site.I came back to try and help. But maybe I should just give up.

[Sam_Spade]

Makin' Do wrote:

Sam Spade- What would be your reasoning for not running the generator below 40F? How would that be harmful?

Not harmful necessarily but inconvenient and not necessary to keep to any fixed schedule. The gas in the bowl evaporates much slower when it is cold.

If it was going to stay cold for a LONG period, I might run it once......but I would much prefer to wait a couple of weeks to hit a warmer spell.

When cold, it takes longer to get up to operating temp.
It also condenses more water in the exhaust system.
It is also harder to provide a good load, at least for me, since my A/C is about all I have that easily gets it above 50% capacity.

And why do you prefer to visit your unit twice when once would work just fine ??? I don't think any additional benefit will be gained by running it a second hour (per the book) OR by doing it more often.

[Sam_Spade]

RJsfishin wrote:
Its not harmful to run the engine when you don't need to. But its not helpful either, no matter what a book says.

YOUR experience with YOUR generator is just that.....one person's experience and does not represent "the truth".

For many types and models of gas engines, especially those with carbs, the gas will partially evaporate and leave a pasty sludge. If left long enough it will harden to something resembling ROCK.

Running some fresh fuel through it periodically usually helps prevent that sludge buildup.

Ignoring the advice of trained qualified professionals is just not wise.

[Canadian_Rainbi]

Makin' Do wrote:
Coming thru the exhaust. Have to try a choke adjustment. Once it's starts it runs just fine.
This unit does not have a prime button.
I never let the starter crank for more than five seconds, and never more than three times before letting I rest.
Owners manual says to run the generator once a month for two hours under half load. I prefer to run it one hour twice a month.
Sam Spade- What would be your reasoning for not running the generator below 40F? How would that be harmful? One thing I'd sure like to avoid is trashing my generator.

The reason for the run time under load is to ensure that all parts of the generator including the alternator and all electronics are thoroughly warmed to drive out any trace of moisture. Running it for a shorter time than called for may not not have the desired result.

[ernie1]

Makin'do:
I have the same Onan you have and I used to always put Stabil into the gas tank and run the generator for awhile before shutting it down. Upon trying to start it after it had been stored for a couple months, give or take a few weeks, it would always backfire VERY loudly and didn't seem like a good thing to have happen.
I have since quit adding Stabil to my gas and instead simply drain the carburetor bowl of the Onan via the drain screw and haven't experienced any more backfiring. I also do not exercise the generator while the rv is stored for long periods of time like 6-8 months or more because my rv is stored inside my garage and the weather in Sacramento is relatively mild. Been doing this for about 7 years or more without any problem.
To make things clear, I still add Stabil to my gas tank, I just don't run it through the Onan.

[RJsfishin]

Its not harmful to run the engine when you don't need to. But its not helpful either, no matter what a book says.
Many things can cause an engine to backfire,... doesn't mean that anything is broke. So it backfired once,.....but still runs good ?? Why you frettin over what ain't broke ?
I start mine only when I need it,.....sets for 3-4 months many times. No prime, starts hard after setting for a month or more.,.....usually starts on the 3rd 5 sec interval. Mine is a big noisy POS Generac !! 360 hrs runs like a new one.....noisy POS !! 🙂

[Makin__Do]

Coming thru the exhaust. Have to try a choke adjustment. Once it's starts it runs just fine.
This unit does not have a prime button.
I never let the starter crank for more than five seconds, and never more than three times before letting I rest.
Owners manual says to run the generator once a month for two hours under half load. I prefer to run it one hour twice a month.
Sam Spade- What would be your reasoning for not running the generator below 40F? How would that be harmful? One thing I'd sure like to avoid is trashing my generator.