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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14984
Experience:  Certified on Onan and Generac generators
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I have an onan 4KYFA26100G in my 98 bounder. I had the carb

Customer Question

I have an onan 4KYFA26100G in my 98 bounder.
I had the carb rebuilt and cleaned, and now it starts fine, but doesn't keep running beyond 3-10 minutes. It will start again after a rest. I have been told everything from a bad low engine switch to a bad fuel pump to fuel filter. I don't know what to do next, since I am not a mechanic. The unit is parked, miles and miles away from help. Can you help? Greg
Submitted: 1 year ago.
Category: Small Engine
Customer: replied 1 year ago.
it's been suggested that I set a new price, but I don't know how to do that.
I am willing to set a higher price in order to get help.
Expert:  Hank F. replied 1 year ago.

There is a link in the email you received. Just click on that link.

Customer: replied 1 year ago.
I clicked the link that brought me here, but there is no prompt to change the price...
Expert:  Hank F. replied 1 year ago.

There are several things that will cause the genset to do this - but the oil switch is not one of them. Your genset doesn't even have one.

While the genset is running, does it run smoothly, or is it surging?

When the genset shuts down, does it just shut down like someone turned it off, or does it start surging?

How long does it have to sit before it will restart?

Customer: replied 1 year ago.
When it's running, it runs quite smoothly.
When it stops, it stops suddenly, as though someone threw the switch.
I have tried it two or three times. The first time it ran about 10 minutes, then stopped.
I tried to restart it immediately, but no joy. It sat about 15 minutes and I could start it again.
The second or third time it ran only about five minutes before it shut down, again suddenly.
I haven't noticed any particular surging - either while running, and certainly not when it stops.
Oh, and when you say "genset", I assume you refer to my Onan Microquiet 4000 generator.
Expert:  Hank F. replied 1 year ago.

The technical term is genset - generator set.

The actual generator is only half the genset - the other half is the engine. I'm not trying to nitpick, but I have to keep terminology correct, as it prevents a lot of misconfusion in testing.

This sounds like you probably have a breakdown in the ignition system. so lets start there.

Run the genset until it shuts down. hen it does, immediately check to see if you are getting spark to the plug.

If you are, let me know.

If not, remove the spark plug wire from the plug.

Remove the small white wire from the coil.

Set your meter to ohms, and place one lead to the ground wire of the coil, and the other to the terminal you removed the white wire from. You should get 0.5 ohms.

Now place one lead to the ground wire of the coil, and the other lead into the spark plug wire. You should get 1,100 ohms.

If either reading are out, the coil is bad. Remember, the coil must be hot when testing, so if you let it sit too long and cool down, you may have to start the genset back up.

If the coil tests good, set your meter to ACV.

Connect one lead to a good engine ground. Connect the other lead to the white wire you removed from the coil.

Press and hold the start button for 3 or 4 seconds. It should read between 15 and 50 VAC. If it does not, the magneto is bad.

Let me know what you find.

Expert:  Hank F. replied 1 year ago.

Was this what you wanted to know?

Customer: replied 1 year ago.
Thanks Hank
We are in the midst of a big winter storm, so I had to put the project on hold. When the weather clears, I will do the tests you suggest and let you know what I find out. Thanks for your patience.
Expert:  Hank F. replied 1 year ago.


Customer: replied 1 year ago.
Hi Hank.
Sorry for the delay. The storms went on and on, and knocked out the power for two days, which means no access to email, or anything internet.
So, yesterday things cleared, (still no power, though) and I went and started the unit, which this time ran only for five minutes. I checked for spark, and saw nothing. (I tried grounding the plug on several spots on the housing, but could not see any spark.) (I had checked the spark cold, and could see a nice steady blue spark).
Then I was going to check the coil, as you advised, but i could not get my probe onto the ground wire of the coil. It is screwed to the bottom screw that mounts the coil to the side of the "start module". I realized I needed a 1/4" socket with torx bits in order to get into the tight place to remove the module, so I could access the bottom of the coil, where the ground wire is.
By that time, the unit was cold, so i tried to start it again, and it wouldn't start at all. I figured I had flooded it with all the looking for spark, so left it alone, and went hunting to borrow a torx socket set.
When I came back, the unit started right up, and this time only ran for three minutes. That didn't even seem long enough to warm up the coil enough to test it, so I gave up and went hunting to borrow a computer to send you this response.What do you think? It seems to me that it's the coil causing the trouble, but I haven't actually tested it yet. The fact that the unit runs for shorter and shorter times after startup is perplexing. At first it was 10-12 minutes, and now it is down to three.I did check the flow of fuel to the carburetor, and it was good, when cold. I was distracted by the other business, and didn't check the flow of fuel when it was hot.I am getting quite frustrated, and could sure use more ideas.Thanks,
Expert:  Hank F. replied 1 year ago.

You have determined that it is losing spark. Yes 3 minutes is enough to get a coil. hot.

Since you are losing spark, you either have a bad coil or a bad magneto.

You do not necessarily need to actually touch the meter lead to the ground wire of the coil (although it is much better to do so), as long as you get a good solid ground.

Customer: replied 1 year ago.
I'm going to carry on tomorrow, since it is dark now.
I will test the coil and the magneto, per your instructions, and let you know.
I have been trying to find these parts online. Amazon has a coil, but i don't find a magneto anywhere…?
Can you direct me to a source? Once I know what I need, I will carry on.
I have been reading some blogs, and the latest one says that the 4KY gen sets are notorious for having problems, and particularly magneto failures. Is this your experience, too or just someone blowing smoke?
Thanks for all your help, Hank, and for your patience.
Expert:  Hank F. replied 1 year ago.

You will only be able to get the magneto through an Onan dealer.

I believe you will only find the coil there, also. I was surprised you said you found one on Amazon, so I looked. I did not see a coil for this unit.

Yes, the magnetos do go out occasionally, but so do the coils. I have replaced many over the years.

Customer: replied 1 year ago.
This morning I went out, with tools and tester in hand, ready to get to the bottom of things, only to find that it won't start at all. Grinds away, but no go.
Aaarrrrgggghhhhh. Any other ideas?
Merry Christmas to you and yours!
Expert:  Hank F. replied 1 year ago.

Check for spark and fuel.

If you are not getting spark, which is what I suspect, test the coil and magneto as I specified.

Customer: replied 1 year ago.
Getting Fuel. Not geting spark, but you said test the coil and magneto when hot, which it isn't since it won't even start now.
Expert:  Hank F. replied 1 year ago.

I said to test the coil and magneot when they were hot, so that they would be broke down and not working. As long as you are not getting spark, one or both are not working, and you can test them.

When it would run for a little bit, they would work when cold, so you couldn't test them cold.

Customer: replied 1 year ago.
Thanks again for your patient explanations.
So, I tested as you specified, and as near as I can read the meter
The first test was good at 0.5 ohms.
The second test, ground of the coil and spark plug wire showed 2800 up to 3000.
That seems like a fail to me...
When I tested the magneto, with my meter at ACV, it bounced around at 8.xx. Not sure if that was 8 or 80, but either way seems like a fail as well.
So, as I read your explanations, I need both a coil and a magneto. Correct?
And you said I need to find an Onan dealer to get those parts.
Is there a directory of sources somewhere?
I guess we are getting to the bottom of the diagnostics, after all.
Many thanks again.
Expert:  Hank F. replied 1 year ago.

I would encourage you to try the tests again. I am not a fan of changing parts that don't need to be changed. Especially when the part is as hardto change as a magneto (the coil is an easy swap).

3000 ohms is way too high - it should only be about 1,100 ohms. If you are truly getting 3000, your coil is definitely bad.

When checking the magneto, make sure one lead of your meter has a GOOD connection to a clean ground on the engine.

At cranking speeds, the magneto should put out somewhere between 15 and 50 VAC,. and should be a steady voltage. If you are getting unsteady voltage, I would suspect you did not have a good connection with one or both meter leads. Also, if y9ou are getting 80VAC, it is very good. That 15 - 50 is the normal range, but higher is ok. It is just lower that becomes a problem.

If you are still only getting 8 volts, it would be 50/50 as to whether the magneto will work or not. The voltage would definitely be low, but may still be enough to fire the coil.

If you are not in a huge hurry, I would suggest changing the coil, and hoping the magneto is working. It isa major job to change a magneto. The genset must be removed from the coach, and be completely disassembled, as the magneto is inside the generator end, under the flywheel.

You can locate your nearest Onan dealer by going to and entering the pertinent information.

Customer: replied 1 year ago.
You're probably right.
I may not have had a good ground when I tested the magneto.
If changing it is such a big job, I will take your advice, change out the coil, and hope for the best.
Wish me luck, and many thanks again.
Expert:  Hank F. replied 1 year ago.

Definitely test them again, just to make sure.

I am going to be signing off in a few, as we have a house full of company. Hope you have a Merry Christmas and a safe New Year.

Thank you for using Just Answer, and please don't forget to leave me an appropriate rating.