Onan 5 KW Generator Won't Start?

[FS2020]

I have an Onan 4.8kw gasoline generator in my RV, Model 5BGEFA26100N, SN H973723191.

It cranks and sounds like it's firing when I hold the crank button down, but when I release the button, the generator shuts down.

Last spring I took it to an Onan/Cummins shop and they got it working. They said "the brushes needed cleaning" or something like that.

We didn't use the RV last year, so the generator sat without being used for a year. Now it's doing the same thing, cranks and sounds like it firing when the start button is held down, but stops as soon as I release the start button.

Thanks for any suggestions!

Frank

[dickandlois]

Frank, sounds like a gummed up carburetor, spray just a little starting fluid into the air cleaner. then try cranking the engine.

It may fire and run just a few seconds, repeat the process. Should it start and keep running keep a close eye on the area of the carburetor. If fuel is running out of it stop the engine.

Let it set for a time, like and hr or so. restart the engine. Repeat the cycle 3 or 4 times. them when you get time add a good carburetor cleaner to the gas tank.

That should clean the varnish and gummy material from the carburetor and float.

Post the results.

Rich.

[FS2020]

I added carb cleaner to the gas and sprayed carb cleaner into the carb, then let it sit for a few hours. I removed the air filter and sprayed starter fluid into the air intake.

It sounds like it's firing when I hold the start button down, but as soon as I release the start button, it shuts down.

I've tried to start it at least ten times, hoping the clog in the carb would clear out, but it hasn't (if it's a clogged carb).

What next?

Do I need to pull off the carb and soak it? I'll verify I'm getting gas and spark first.

Thanks,

Frank

[dickandlois]

Frank,

Sounds like the needle valve in the Carburetor is stuck. happens when they set with no fuel / stable in the bowel.

Fuel should try to work its way into the carburetor.

Just let it set, then keep trying to get it to run. Once that happens, keep an eye on the carburetor for leaking fuel. stop the engine and let it set some more, things could just clean them selves with time.

See if the problem will clear before getting into the carb.

Rich.

[elkhartjim]

I hope you get it started without a great expense and I know this is kind of like closing the barn door after the horses get out; all generator manufacturers recommend starting and runnig the genset for at least 30 minutes under at least 50% load monthly. That eliminates this problem along with helping the armature, etc function when needed.

[FS2020]

Frank,

Sounds like the needle valve in the Carburetor is stuck. happens when they set with no fuel / stable in the bowel.

Fuel should try to work its way into the carburetor.

Just let it set, then keep trying to get it to run. Once that happens, keep an eye on the carburetor for leaking fuel. stop the engine and let it set some more, things could just clean them selves with time.

See if the problem will clear before getting into the carb.

Rich.

Thanks Rich, I just made a mixture of 8 oz of fuel injector cleaner (enough for 20 gallons of gas) and 8 oz of gas. I fed it through the fuel intake line. So the carb bowl is full of concentrated fuel injector cleaner and hopefully it will dissolve the gum. I will let it sit for a few hours and try it again. Thought I would try that before taking the carb off. That also verified that the fuel pump is working.

Will let you know the results. Frank

[FS2020]

I flushed the carb with concentrated fuel injector cleaner and let it sit for 24 hours. I've verified that it's getting gas and the fuel pump works, it's getting spark, it's getting 12.7 V from the batteries.

I tried several times a day for several days to get it to start.

So I've given up and scheduled an appt with Cummins Onan near Pittsburgh. It's a one hour drive each way. Last year it cost me $150 to fix this problem.

I will post what the Cummins Onan tech's say was the problem.

Thanks for trying to help!

Frank

[kaypsmith]

Onan generators have a safety feature, if the generator doesn't excite, and start producing ac current, it not continue to run. That is probably why brush cleaning worked last time, and hope that it will work again.

Best solution, start the generator on a regular basis as recommended, and run at half load for a period of time, "30 minutes" recommended by most people in the know. This helps keep the carburetor functioning well, the brushes cleaned, the brush springs from corroding and sticking and also moisture from deteriorating the stator/ windings.

Happy trails, hope for an easy fix.

Kay

[FS2020]

OK, I got the generator to start! But it sounds like it's running at full speed so I shut it down after a few seconds.

I'm thinking the linkage that controls the carb is stuck? Any other thoughts?

I agree completely with Kay: I need to run the generator on a regular basis to keep the brushes and carb clean.

Thanks everyone!

Frank

[dickandlois]

Frank, Running is a good start !

Look at this link, and see if the manual matches you unit. closest I could come to your model number.

http://www.cumminsonan.com/www/pdf/manuals/965-0530.pdf

If it does, look a section 6-page 11 that section covers the governor.

The manual is 120 pages.

Rich.

[FS2020]

Thanks so much for the service manual Rich! I had been trying to find it for a long time.

I started it again and let it run for awhile and the engine speed gradually slowed down to normal. It ran for about 20 minutes then shut down.

I'm hoping I've brought it back to life, with good advice from this forum.

Thanks,

Frank

[wolfe10]

Frank,

If the RPM sounds high, voltage is high or HZ is high, be sure the two breakers on the generator are OFF so you don't harm anything else on your coach.

And, absolutely make sure the linkage is totally free. Once removed a mouse nest from a guy's generator-- was holding the throttle open and over-speeding the generator.