Onan 4000 Generator not quite starting - Probably a fuel issue

[Tiercel]

My Onan 4000 gas generator sounds like it is starting, but it immediately dies as soon as I release the starter. I am barely beginning the process of introducing myself to the generator since acquiring this MH. I have no clue how long since it ran last. I know the basics about gasoline engines but have no manual for this specific generator.

I primed it by pressing the prime button (it apparently has an electric fuel pump). Gas dripped ( have plenty of fuel in the tank). I think it was from flooding and not a leak. I removed the air filter and gave it a shot of starting fluid. It started for a few seconds with black smoke (I assume because it was flooded). This means it is getting spark though the outside of the sparkplug looks OLD. It could be original since it has less than 200 hours of runtime.

I will pull the spark plug today to see what it looks like. I will see how difficult it is to drop the sediment bowel and check for trash, water, or a stuck float. I guess I could shoot some SeaFoam carb cleaner in it. I guess I will search online for a manual.

I have no idea what the altitude adjustment is. I assume it changes the air mixture. It was set at 10,000 ft, and we are at less than 100 ft sea level.

 

[SeilerBird]

Onans have lousy carbs. I would start by rebuilding it.

 

[DonTom]

My Onan 4000 gas generator sounds like it is starting, but it immediately dies as soon as I release the starter.

That means the control board is shutting the genny down for a problem, such as running too fast, too slow, voltage wrong, etc.

Look at the red light on the start switch on the genny. If it blinks three times after you try to start, it means a code is set. If so (and most likely is) a fast push towards "prime" will make it blink the error code. For an example, a code "24" (or whatever number) will blink twice and then four times and repeat the "2-4" three times and then give the next error code (if any).

Get that code (or codes) and mention the number(s) here.

-Don- Reno, NV

 

[DonTom]

have no manual for this specific generator.

Get that here, for free.

-Don- Reno, NV

 

[Henry J Fate]

New plug, new air cleaner, new oil for starters.

If it has been sitting, pull the carb and clean it. Remove the bowl and the needle valve assembly and clean all that up. Use the carb cleaner straw and spray out every passage way. Remove the main jet and carefully clean that out. If it has a removable slow jet, pull that also. Clean both jets and their passage ways.

Depending on the history, many times it is possible to bring the carb back to life without any new parts.

Onan factory carburetors perform their duty very well. I have used several all needing to be cleaned from sitting. Never replaced a part but if you do need parts, use cummins/onan factory parts.

The fact that the generator has only 200 hours is not a factor in the above maintenance.

 

[DonTom]

It was set at 10,000 ft, and we are at less than 100 ft sea level.

That will make your carb run way too rich. Set it to around sea level, as low as it will set.

-Don- Reno, NV

 

[DonTom]

use cummins/onan factory parts.

I use a cheap $40.00 Chinese carb in mine, works perfectly and IMO, is better built than the Onan, at least in some ways. In my Onan carb, a small pin broke to the butterfly flap. The cheap Chinese carb uses a thick shaft there that will not break!

Also, do NOT use the recommended Onan Champion Spark Plug! See here.

-Don- Reno, NV

 

[Henry J Fate]

10-4 on that onan spark plug

 

[uchu]

+1 on the carburetor.

That's my project for spring, as soon as I pick George up from storage.

I'm replacing it; not going to bother trying to clean it up.

 

[JayArr]

For the cheap price chinese carbs sell for it makes sense to have a "spare" carb with you. They swap easy and can be used to troubleshoot and get you running right away if that's the problem. When you have two you can rebuild the "spare" at your leisure.

 

[DonTom]

New plug, new air cleaner, new oil for starters.

IMO, we should not guess at such issues before getting the code from the genny.

However, I must admit guilt there myself. But before I knew better.

Say I was trying to fix an issue and put in one of those Champion spark plugs . . . Now even if I fix the genny's first issue, it still will not run. That can cause major delays in the repair.

I have also seen many others break things more that they were trying to fix. And even with NEW parts.

IMO, fix it first by using the code. Then if you want to change other stuff, do it, one item at a time, making sure it all works fine after each and every change.

-Don- Reno, NV

 

[DonTom]

For the cheap price chinese carbs sell for it makes sense to have a "spare" carb with you.

Thanks for the reminder, I meant to do such myself. But I wanted to buy one first to see how it worked and after I got the genny running, I forgot about buying a spare.

BTW, I gave the cheap Chinese carb a five star review on Amazon.

Before I bought it, I saw several warnings here about using the cheap carb. But at $40.00, I was willing to risk it. Perhaps they improved them over the years. But all I can say for sure is my genny could not run any better than it does now with the $40.00 carb.

I can even say I trust it more so than the Onan. At least I know that pin to the butterfly will not break!

-Don- Reno, NV

 

[_Rusty_]

my neighbor had similar issues last spring with first time out after storage (start but won't run). local service found blockage from mice nest in carb. i was reading about it before he got serviced, and found a safety cut-off related to low oil. hope you find it quickly!

 

[Tiercel]

Life snd weather got in the way, and I could not get back to my Onan 4000 J until today. I am starting by re-reading all your posts.

My BiL did not do maintenance other than taking it to a good garage that probably only serviced the chassis. So I will start with an oil change, spark plug check (likely replacement), and cleaning the sediment bowl. If that does not at least get it started, I will proceed with cleaning the carb as Henry Fate outlined. If I can get it to start, I will clean out the spark arrestor, which was likely never done.

Thanks to DonTom for the link to the manual. What a huge help! I will also order the Chinese carb as soon as I am confident I am getting the correct one for this generator. At that price, the carb seems like a no-brainer even if I get it running without it.

PS: At this point, I don't think I have any blink codes.

Some simple questions:
1. On spark plug replacement. Should I take the old plug to NAPA or even AutoZone to buy a few replacements to keep on hand? Are there any words of wisdom other than Champion can randomly;y fail when still fairly new?

2. I have not looked at the starter wires yet to see whether they route to the chassis battery or the coach battery. The starter is not an issue, but inquiring minds need to know.

 

[DonTom]

At this point, I don't think I have any blink codes.

My Onan 4000 gas generator sounds like it is starting, but it immediately dies as soon as I release the starter.

Above makes me think you do have a code. Could the red light be burnt out in the genny switch?

Or could the switch be broken as mine was? See the photo in message 36 here.

As for the spark plugs, use NGK BPR5ES. Yeah, keep a couple of spares also. See message 25 here.

More than likely, your genny only uses the house battery to start, as does mine.

-Don- Reno, NV

 

[Tiercel]

…Could the red light be burnt out in the genny switch?

Or could the switch be broken…

As for the spark plugs, use NGK BPR5ES.

The light on the switch works and the switch primes the carb. I will double check for codes after I change the plug and do a few basics The Gen never totally starts but it fires and starts to spin but dies the instant I release the starter.

BTW - why did you specify that particular plug? The plug that was in it is an RN14YC. It looks decent but it is likely 20 years old.

The manual doesn’t not seem to identify a specific plug or a gap setting.

 

[DonTom]

The plug that was in it is an RN14YC.

See here. Especially see message number 23.

The Gen never totally starts but it fires and starts to spin but dies the instant I release the starter.

That is because when you're trying to start, the control board cannot shut down the genny from a fault until you let go. Then the fault shuts down the genny. So that is why it sounds like it is trying to start but always dies when you let go. That also tells me a code was set and should be blinking your red light. That is if the red light works as it should.

BTW, take out your Champion spark plugs and put them where they belong. In your trash can.

-Don- Reno, NV

 

[DonTom]

The manual doesn’t not seem to identify a specific plug or a gap setting.

Onan expects you to use the Champion you're using--but don't!!!!

The gap should be .025" (.635 mm).

-Don- Reno, NV

 

[Tiercel]

Thanks for the spark plug reply, DonTom. I appreciate your responses and help.
For what it's worth, I just heard from a mechanic and one other guy on Youtube that Onan carbonators are non-serviceable according to the mfg and his own experience. At the cost of the Chinese one, I have to say they are hardly worth the effort to service.

BTW, does anyone use this stuff? The price is a little nuts. https://www.amazon.com/Cummins-3265...01-20&linkId=262e6eef5a005a6892efd7ec2b696b4c

 

[DonTom]

BTW, does anyone use this stuff?

In your 4K genny, use cheap plain 30W engine oil. Any brand you want.

-Don- Reno, NV