Onan 4KY generator hard to start

[SJMaye]

My generator will start, but not as readily as I would like. When starting cold it takes 3 priming / starting attempts before it fires off and continues to run. After it has run a while it will start with just 1 prime.

Has anyone here had this issue before?

[16ACE27]

Define "prime". How long do you prime it? 30 - 45 seconds is the norm.

[ghnl]

How often do you run the generator? I've seen advice saying it should be run as much as 30 - 60 minutes once a month. I run ours for 20 -30 minutes once a month during the 'camping season'. At the end of the year I treat the (full) gas tank with Stabil, run the generator for 20 minutes and then I shut off the fuel supply (I installed a shut off valve in the fuel line to the carburettor) & let it run the carb dry. There is also a drain screw on the float bowl but you'd need to be ready to catch the gas. It is my experience that today's gas does not store like it used to back-in-the-day.

P.S. Hello & welcome!

[EA37TS]

On my gas generators to prime you held stop until the start/stop light went out and then you pressed start. Forest River and Thor were both the same procedure.

How long are you holding stop to prime?

[SDMiramar]

Had a similar issue on a previous toy hauler. When was the last time the fuel filter was changed? Once I changed the filter on it, it seemed to fix the same issue that I was having on mine.

[MJC62]

Welcome aboard!
That seems normal to me depending on how long you prime and how cold it actually is.
Ours we prime till the light goes out and then crank it for 7-10 seconds. If it doesn't start, we reprime and it usually fires on the second attempt.

[SJMaye]

Originally Posted by 16ACE27

Define "prime". How long do you prime it? 30 - 45 seconds is the norm.

There may be the problem. I just bought this RV used and followed the previous owners instruction. I press Prime until the LED lights and then press Start. It is nowhere near 30 seconds. More like 5 seconds maybe. I was afraid to go longer for fear it would flood the engine.

To answer another question as to how often I run it, I don't know about the previous owner, but I have been running the generator almost daily for 10 - 20 minutes. Just trying to exercise it.

My lack of knowledge. Looks like I am the problem.

[ghnl]

Using the 'prime' function for a little longer will not hurt anything. The float bowl in the carb has a shut off valve to stop the fuel when it is full (very much like the toilet tank in your house).

Running the generator (or any internal combustion engine) for a short length of time can be worse than not running it. The short run time does not get everything up to full operating temperatures. A normal byproduct of combustion is H2O. That, plus condensation, becomes a contaminant in the oil. When the engine is run for longer periods the heat will get rid of that contamination.

[OldWEB]

Originally Posted by SJMaye

My generator will start, but not as readily as I would like. When starting cold it takes 3 priming / starting attempts before it fires off and continues to run. After it has run a while it will start with just 1 prime.

Has anyone here had this issue before?

I used to have this problem until I discovered my choke would stick in the "open" position, it would not close after running hot when the unit cooled down. A simple push to the left always reset it (when cold) and ready for the next remote start. It always travels freely after that, just sticks after running it.
Found this:
https://www.irv2.com/forums/f84/onan...lp-414545.html

[SJMaye]

Originally Posted by OldWEB

I used to have this problem until I discovered my choke would stick in the "open" position, it would not close after running hot when the unit cooled down. A simple push to the left always reset it (when cold) and ready for the next remote start. It always travels freely after that, just sticks after running it.
Found this:
https://www.irv2.com/forums/f84/onan...lp-414545.html

Thank you. I will check this out next.

[SJMaye]

Originally Posted by ghnl

Running the generator (or any internal combustion engine) for a short length of time can be worse than not running it.

How long should I run it?

[ghnl]

Originally Posted by SJMaye

How long should I run it?

10 minutes is not enough. 20 might be the minimum during warm/hot weather, 30 - 60 minutes when it's cold outside.

It's also advised to operate some electrical loads so that those parts of the generator are also fully warmed up to drive off moisture (condensation). In the summer run the A/C, if it's cold perhaps an electric heater.

That advice to check the operation of the choke is good, too.

[ghnl]

So, even though the Generator in our RV is working well, I thought I have a peek at the choke operation.

Can anyone help me understand this statement? "Slowly rotate the adjustment plate until the bi-metal choke shaft connection is visible in the sight window." I understand the rotate part but is the 'sight window' the tiny 1/8" hole near the top? Onan positioned this such that one cannot get a direct view. If the removable panel was a couple of inches wider it'd be easy to access.

[OldWEB]

That is the sight window according to the service manual. I have not tackled mine yet, but it was mentioned to use a bore scope camera to view thru it... dunno.I need to determine what is hanging up inside mine... or maybe just mark the present setting and operate the adjustment thru its total span, maybe that would loosen it up for me. Can always return it to the present setting.

[Jimbo56]

To the OP, when you press the stop button. The priming process doesn’t start until the red light lights up. I then have to hold mine for a 60 second count. The Onan 4000 in mine is up front. The gas tank is in the back. That’s a pretty long priming run. Back in the old days, automotive carburetors had a little diaphragm that held pressure and kept the fuel from running back to the tank. I think this is called an accelerator pump. The diaphragm getting a hole in it would sometimes cause the vehicle to be hard to stop. At some point, when my eyes are working, I’m going to investigate this in my Onan. But for now, I start it, turn on tv. Crack a beverage. And watch March Madness bball for a while. Shoulder surgery on 4/1 will drastically put my recreational plans on hold for a bit. But I’ll still exercise the genny.

[EA37TS]

Originally Posted by Jimbo56

To the OP, when you press the stop button. The priming process doesn’t start until the red light lights up. I then have to hold mine for a 60 second count. The Onan 4000 in mine is up front. The gas tank is in the back. That’s a pretty long priming run. Back in the old days, automotive carburetors had a little diaphragm that held pressure and kept the fuel from running back to the tank. I think this is called an accelerator pump. The diaphragm getting a hole in it would sometimes cause the vehicle to be hard to stop. At some point, when my eyes are working, I’m going to investigate this in my Onan. But for now, I start it, turn on tv. Crack a beverage. And watch March Madness bball for a while. Shoulder surgery on 4/1 will drastically put my recreational plans on hold for a bit. But I’ll still exercise the genny.

A few years back Onan had a bad lot of 4000 carbs that did have a hole in the diaphragm. There were numerous posts on the forum about issue especially with the Axis/Vegas, For Winds and Chateau. I had the issue on an earlier Forest River Sunseeker. There was also an issue of vapor locking because of access heat where manufacturers, not just Thor, had to put screen mesh in the generator compartment doors.

[Jimbo56]

Originally Posted by EA37TS

A few years back Onan had a bad lot of 4000 carbs that did have a hole in the diaphragm. There were numerous posts on the forum about issue especially with the Axis/Vegas, For Winds and Chateau. I had the issue on an earlier Forest River Sunseeker. There was also an issue of vapor locking because of access heat where manufacturers, not just Thor, had to put screen mesh in the generator compartment doors.

I’ll investigate and tear into it at some point.

[16ACE27]

There's no accelerator pump or diaphragm in small gasoline engines carburetors like those used in generators, including the Onan 4000 and 5500.

Some small engines use a vacuum operated pulse pump with a diaphragm if the fuel source is not sufficiently above the carburetor for gravity feed reliability.

The Onan generators use an separate electric fuel pump to feed the carburetor from the combination fuel tank in the MH.



A rebuid kit has no diaphragm, only gaskets, O-rings, jets, etc:

[EA37TS]

My mistake, not carbs but fuel pumps were the issue a few years back. Went back to the Sunseeker notes. Diaphragm is in the fuel pump and not the carb.

[Eeyore]

Originally Posted by SJMaye

My generator will start, but not as readily as I would like. When starting cold it takes 3 priming / starting attempts before it fires off and continues to run. After it has run a while it will start with just 1 prime.

Has anyone here had this issue before?

I have the exact same issue... takes at least 3 prime and start sequences and then runs normally after that. Usually run monthly when the RV is not in use. Seems to start fine if ran within the past week.

Generator has 130 hours and is 5 years old. I have changed the fuel filter a few times since I have owned it (bought used in 2021).