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Old 08-30-2016, 11:54 AM   #1
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4000 onen micro- quit, year 2000, gen set - dumb move

I had not exercised my generator for about 6 weeks and it was hard to start so when I finally got it running I decided to spray some gum out through the carburetor to help clean it out. Because it was so hard to start I decided to take the air filter off when it was running, a procedure I had used in the past. BUT!! I dropped the nut and I think the washer holding the air filter on and either one or both got sucked into the carburetor.

Now I have a generator that starts and runs great but sounds like a thrashing machine. Can anyone give me some advice? If the valves or something got seriously damaged I assume it would not start and run???
My next step is to remove the carburetor to see if I can find and remove the nut and/or washer.
Or am I totally screwed and will need to do a major generator motor overhaul? We are still on our road trip and I have not had a chance to check with a mechanic.
My dumb move really has me bummed out.

Thanks in advance for any information!

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Old 08-30-2016, 12:12 PM   #2
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More than likely that nut made it through the valve and is now in the combustion chamber hammering the top of the piston while running. My advise...stop running that gen immediately and get it serviced. If running well as you say, it might be as simple as pulling the cylinder head off, removing the nut and installing the head back on with a new gasket and possibly a spark plug.

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Old 08-30-2016, 02:58 PM   #3
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How big was the washer , Dime, Quarter?? How loud is the racket???

It could be trapped in the intake, between the carb and the cylinder. Pulling the carb and the intake tube that attaches between the carb and the cylinder, you should be able to see it.

If it made it into the cylinder, I would have thought that it would have destroyed the spark plug. Pull the spark plug and use a small bent wire Piece of cloths hangar) fell around inside the cylinder.

I have the Onan manuals on my site. You can download the Onanparts manual here:

While your at it, replace the plug and the air filter....
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Old 08-30-2016, 03:38 PM   #4
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Thanks for your advice!! We have a 2000 Yamaha portable generator for a backup so we are not running the coach generator on this road trip. I will post the final outcome after our return home in October.

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Old 09-01-2016, 07:27 AM   #5
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Take a look

I bought one of the little borescope type cameras with a micro USB connector from Amazon. They are self illuminated and come in various lengths, or add on extra cordage as needed. Great for looking inside engines or air conditioning ducts. I have taped it to a fish tape for getting cables run thru walls and attics so I can see where my ends are. Under 20 bucks! They can connect to your iPad or android phone.

Remove your spark plug, and have a look. My bet is your nut and/or washer is in the combustion chamber, and you will have to remove the cylinder head. Maybe just use a very flexible magnetic probe.....but I am thinking not. Best to open it up and see first hand what may have been damaged. Especially if you put some hairline cracks in the piston. Not too difficult if you are somewhat handy and know how to use a torque wrench. With a bit of luck, and a lot of prayer, maybe all you need do is to remove the stuff you decided to!
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Old 09-01-2016, 08:24 AM   #6
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Pull the cylinder head off.
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Old 09-25-2016, 05:21 PM   #7
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Wow why only so few hrs pull carb then head good luck

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