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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14900
Experience:  Certified on Onan and Generac generators
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i have a onan 4000 genset emerald plus...model #4bgefa26100j

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i have a onan 4000 genset emerald plus...model #4bgefa26100j ser # XXXXX
the generator worked fine last week, then today i went out to the rv to cool it off and started the generator and it started fine. it ran for a minute then all of the sudden started running rough. finally it stalled.
i restarted it and it ran again for a few seconds then shut off. now it wont restart at all.....i checked the spark and it seemed to be very weak. it is getting fuel. can you guide me?
also i checked voltage while cranking at j4 pin 7 and it was just over 9 volts.


I truly apologize for taking so long to respond, but I was out of town for the weekend. Where I was at, we did not even have cell phone service, so I was REALLY out of reach.

Did you check for spark at both plugs, or just one?

This particular set has a bad habit of burning the inside plug.

They also do not have as strong a spark as you would think it should, so the quality of the spark may not be an issue.


Check the spark at both plugs and let me know how they look.

Also, when was the last time you did a good tune up on this set?


Customer: replied 7 years ago.

i have only had the rv for a year, but i had the generator carb replaced and the plugs then.


well after i asked the question i let my neighbor borrow the rv.

when he returned the next day i decided to just try the generator for curiosity.......and it started after a few moments it settled down and ran fine.

i have no idea what happened.

do you have any idea what caused this so i know if it will happen again when we go camping next weekend?

The 3 most likely causes of this are going to be:

1. Dirty/old fuel.

2. A loose wiring connection.

3. A fuel pump starting to fail



When I see intermittent symptoms like this, it is usually associated with the set not being exercised regularly. Letting the set sit without being ran is very bad for them, and can do some really strange things to them.

These sets need to be ran at least once a month, for 30-45 minutes with a load on them.

This ensures that the fuel is always as fresh as possible (bad fuel making the carb go bad is the number 1 problem with these sets), the brushes and slip rings are prevented from corroding, the set is kept clean, and the oil system keeps oil in it.


If it is running good right now, I would add some Sea Foam to the coaches fuel tank (assuming this is a gasoline set), and run it as much as possible on your next trip.

If you would like, I can give you some general preventive maintenance items to do that will only take about an hour.


Customer: replied 7 years ago.
yes i would like the pm items to do......also how often do the brushes need replaced?

1. Brushes have no 'set' schedule for replacement. There are too many factors that can affect wear. The only thing you will have to go by is the brush length when doing your PM.


2. PM should consist of the following:

Spark plug check/cleaning/replacement as necessary. Gap should be .025"

Air filter check/replacement (never clean one) as necessary.

Blow off entire genset with compressed air - never use water to clean.

Check brushes and slip rings.


To do so: Remove the air cleaner. Directly behind the air cleaner is the end bell of the generator. In the middle of the end bell is a rectangular plastic cover. Use a flat tip screwdriver to pry it out and expose the brush block.


In the center of the brush block are 2 round holes with a single bare wire coming out of them. These are the brush leads. Use a small diameter probe to stick down in these holes until it hits the brush. Mark the probe where it is flush with the brush block. Remove the probe and measure from the mark to the tip of the probe. If this measures 1" or more, the brushes are worn and must be replaced.


Leaving all wires hooked up, remove the 2 screws securing the brush block by turning each screw about 4 turns at a time. The brush block must come out straight, as it is made of ceramic and is very fragile. Be very careful to not drop the screws. It can be harder to get them out than to get a lollipop from a 2 year old. Use the wires to hold the brush block and guide it out.


Examine the brushes. They should not have any chips or cracks and should be worn in a smooth arc pattern. They should slide freely in the slots in the brush block. Clean the brush block with electrical contact cleaner.


Now examine the slip rings. They are the 2 bands that the brushes ride on. They are made of copper and should be as shiny as a new penny. They should be smooth and not have any scratches or pits. If they are dirty, clean them by attaching a piece of scotch brite pad to the end of a small stick and holding it to the brushes. Remove the spark plug wires and press start to crank the set and make the slip rings turn. WATCH YOUR FINGERS!



Adjust valves per the schedule in your owner's manual. The intake valves should be set to .005", and the exhaust to .013"


I have attached a copy of the Owner's Manual maintenance schedule for you, if you do not have it.

Click here to download it.


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