Onan 4000 Start Runs and Dies Issue

Stupid question, but do you have enough gas in your tank ? Most generators won't run if it's down around a quarter tank, but you probably know that.

How long has it been since the generator was used, and worked properly? Was it Exercised monthly since then? Do you treat your gasoline with Stabilizer?

It doesn't take long for varnish to build up in an ONAN carb, and the slightest bit will really louse it up. There are ecopolitical reasons whey ONAN doesn't offer carb repair/rebuild kits but the fact is they (I'm thinking the KY series ONAN) carbs are very difficult to clean.

My guess is there's crud in the "idle" passages. Remember, an RV GenSet is a fixed-RPM unit. 3600 if it's a KY which I expect it is. That means the "Idle" circuit has to work all the time. Some KY series had a Low Oil Switch, but later Spec Codes deleted them as they were troublesome.

Post the full Model Number (last character is Spec Code) and we can find you a Service Manual. No point in blaming and testing an Oil Switch you don't have.

The genny gurus hang out on the Tech Issues Forum. Might be a good idea to hit "Notify Moderator" and ask this to be moved there.

The Onan generators have circuitry that shuts down the generator if it is not operating properly.

Bad fuel pump.

I had this one time ,run stop had to buy a new carb.

Mine was also a bad fuel pump If you push the primer switch and it has a continuous ticking sound it means the fuel pump isn't picking up fuel

I do not put in fuel stabilizer. The fuel pump is working cause when carb was off I primered it and fuel came out without an issue. It is a 4000 ky series.
My plan was to warm up the genny then change the oil. I was not able to get it up to temp. I am going to change the oil and try it again.

P.S. new plug and air filter is clean. I am a bit lost on how to determine if the solenoid is bad on the carb. Or how to determine if this is non carb related. Since it is colder where I am at still about 55. Can I adjust something on the carb to see if it runs better maybe something got out of wack from driving?

Thanks again for all help and info!!

Okay, It got a little warmer today so I tried to run the generator again. It will just keep revving up and down and up and down.

I do not know what is up with that/ I am thinking that even though the carb looked clean when I had it off I need a new one?

Extremist wrote:
Bad fuel pump.

Yes it is.

You can try treating it with a very strong dose of Seafoam carb cleaner. Find a place where you can cut the fuel line between tank and pump that'll be easy to re-connect. Mix about 50-50 Seafoam & gas in a can. Get it thru the carb by taking the fuel line loose from the carb and running the pump on 'prime', then running the Onan. Obviously be careful of open gas can & sparks.

Let it sit 12 - 24 hours, than run it a bit to freshen the solvents. Repeat. I had to do this daily for about a week to fix a neglected 2800 0nan, but it eventually worked. Saved me about $400.

Jim, "I've taken a vow of poverty. To annoy me, send money."