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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 15198
Experience:  Certified on Onan and Generac generators
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My Onan Generator is a 12.5 JC-C3R/9616 AA. It starts easily

Customer Question

My Onan Generator is a 12.5 JC-C3R/9616 AA. It starts easily and runs for 10-15 minutes then it acts like someone turns it off then on in a seconds time. Then it runs for maybe 5 minute more and completely stops. just like it's turned off. I can restart and it might run 2-3 more minutes and stop again. It can't be restarted without waiting 15-20 minutes then the cycle starts over again. That would seem like an ignition electrical problem but I don't know what part to blame.
Submitted: 1 year ago.
Category: Small Engine
Expert:  Hank F. replied 1 year ago.

Hello, my name is ***** ***** I am going to assist you with this.

What fuel is this unit running on - gasoline, LP or NG?

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

What I need you to do is to start the unit, and let it run until it shuts down. When it shuts down, and will not restart, check to see if you are getting spark to the plugs.

Are you?

Customer: replied 1 year ago.
The unit runs on natural gas.
While the unit is running speed is very stable and voltage is stable until it drops out for an instant then it recovers nicely.
The unit is outside with an Onan weather housing. It's very difficult to get inside but I might be able to pull one of the spark plug wires and see if spark is available when trying to restart. I'll try to check that as you suggest and get back to you.
I had a thought when looking over the wiring diagram. It shows a high temperature switch that is on some models. It's mounted on the optional air shutter assembly. I am not sure if my machine has the air shutter assembly as I can't really get a view of that side of the machine. It's pretty obvious that if that high temperature switch is there and it opens for some reason the machine would stop. That might explain why waiting 10 or 20 minutes would let it cool down enough to restart.
By the way, as you might guess, I do have the service manual for the generator/engine.
Expert:  Hank F. replied 1 year ago.

Yes, a high temperature switch can cause the unit to shut down and not restart until it cools.

But so can other things, such as a coil that is breaking down. It is much more common for a coil to go bad.

Let me know what you find.

Customer: replied 1 year ago.
Today was a little cooler like maybe 5 degrees. I was going to test the spark using the spark plug out of my lawnmower and removing one of the spark plug wires I could reach. I let the machine run for over 45 minutes and it didn't burp once. Go figure. I ran out of time so this test is going to have to wait another day and I may not be able to get to it tomorrow. Tomorrow it's supposed to be a bit warmer but it's also supposed to rain. Standby and we will see how it develops. I really don't think the machine has a high temperature switch. At least I don't know where it is.
Expert:  Hank F. replied 1 year ago.

It is possible that you have a bad spark plug or 2. It would be pretty uncomon for one to run good for a while and then quit, but is possible if it is cracked.

Customer: replied 1 year ago.
This machine is old enough I am giving thought to changing the plugs, wires, coil, distributor cap, and rotor. My desire to do that would be enhanced a lot if it were easier to work on the engine. Getting the cover off of the weather housing will be the worst part of the project. One of the cylinders is miss firing but that doesn't seem to effect the over all speed and it's not causing the engine to shut down. It's been a long time since the engine has had a tune up. That's a long time in years but not hours running time. Since the last oil change a year ago the engine has had only 5.25 hours of running time but it's probably been 10 years since the engine has any kind of a tune up.
Expert:  Hank F. replied 1 year ago.

Yes it's definitely time for a tune up.

Parts go bad from just sitting, too.

Expert:  Hank F. replied 1 year ago.

Was this what you wanted to know?