Onan Backfire - Not A Good Thing

Do you push the prime button first?

Through the carb is too lean, through the exhaust is too rich.
Automatic choke may need slight adjustment if it happens again.

Makin' Do wrote:
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?

When my onan started backfiring it then surged. Later it would not start. In my case the exaust valve spring broke causing backfire start up then surging. Then the spring lock fell out causing a no start. This happened weeks apart.

Makin' Do wrote:
When not traveling I run my Onan 2800 for one hour under a 1500w load every other week.

I personally think that once a month (4 weeks) would be plenty AND I would avoid doing it altogether when the temp is below 40 F.

Does it have a prime button ??

You maybe fed it beans? Something is WRONG. The carburetor should have had enough gas level to start three seconds after pressing the start button.

Do these gens have flicker points or electronic ignition? I used to TRASH OEM capacitors and replace them with a high voltage capacitor.

Do whatever it takes to FORCE the fuel pump to fill the carburetor before you touch the start button. If the engine then starts quickly you have your answer. Cranking and cranking makes rebuilders and parts store owners very happy.

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.

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:
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.

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.

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.