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Onan Generators

Quick help with Onan 12.5


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  #61  
Old 03-19-2017, 02:15:54 PM
Ben Cowan Ben Cowan is offline
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Default Re: Quick help with Onan 12.5

might as well get it. If you dont use it. youll probably help someone else by having it in hand! thats still a cheap price!
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  #62  
Old 03-19-2017, 04:10:39 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

I had the generator inning today for 45 minutes give or take. Got it good and warm and did some checks. The pictures are all from today.
I also turned the blower housing to the exhaust side so all the hot air goes one direction.
The one thing I noticed after it ran a while, ice formed on the intake manifold right where the carb bolts up and it tees off left and right. This one does not have the air preheater since it is dual fuel or vacuflo cooling, not sure which.
With what I saw today, I now have no problem doing whatever work is needed to this unit.
Something else I checked today, with it running and warmed up, I pulled off the crank case vent line from the intake. It still has a little vacuum on the crank case side.
So I will get the new stuff ordered for the run / stop solinoid and start doing a good cleaning inside and out. After I get it all figured out and cleaned up, I want to get the gaseous stuff to hook it up that way too.
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  #63  
Old 03-19-2017, 07:04:16 PM
Max Thompson Max Thompson is offline
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Default Re: Quick help with Onan 12.5

Give him the $25. The relay and socket will cost close to $20 by the time you pay postage.

It is not worth $5 to do the work to change it over.
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  #64  
Old 04-01-2017, 03:36:30 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

I installed the new style relay today and now rhe generator won't start. I believe it is a fuel problem but not sure. Question, for testing, would it hurt to run a jumper 12 volt hot wire to the coil? I would only do this for a short time just to get it running then start my trouble shooting once it runs.
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  #65  
Old 04-01-2017, 04:14:56 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Quick help with Onan 12.5

Before I would do that, I would check that you are getting voltage to the + side of the coil while cranking and that the propane electric solenoid valve is getting voltage and is actually opening up.
Just my thoughts.
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  #66  
Old 04-02-2017, 04:03:35 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

Okay, I have it down to a wiring issue. Actually a low voltage issue. The big problem I have is that my set has an over temp sensor that is wired in to the centrifugal points somehow. I have looked at the diagram for JC units and mine is not wired like that. I looked at 967-0500 books and mine is different. I am only getting 2.5 volts at the centrifugal points at the bell housing. I have it traced back to the control box and have the same voltage there. I need to do more tracing but the wire diagram is about useless as it is different then mine. Does anyone have a different wire diagram for the latter JC units? Mine is spec AB.

Forgot to add, If I apply 12 volts to the centrifugal switch the unit runs and stops as it should. So my problem is just getting 12 volts to feed the switch.
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  #67  
Old 04-02-2017, 09:34:22 PM
Max Thompson Max Thompson is offline
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Default Re: Quick help with Onan 12.5

According to the build sheet, the correct diagram should be attached.
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File Type: pdf 12.5JC-3R 10259AB.pdf (19.6 KB, 17 views)
File Type: pdf 612-5564 C.pdf (159.6 KB, 19 views)
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  #68  
Old 04-03-2017, 06:12:55 AM
Handyhiker1 Handyhiker1 is offline
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Thumbs up Re: Quick help with Onan 12.5

Max,
I am not out by the generator right now but that sure looks like the right diagram. Thank you very much. Maybe now I can figure this thing out.
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  #69  
Old 04-03-2017, 05:00:53 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

Life is GOOD!! With the new diagram I was able to trace the wires and find the bad connection. Fixed it and now all is good. It starts as it should and stops with the switch. The starter cut off works when it starts and all seems good. Now I have 2 more things to get and then tune up and clean up. I still need to find a new main jet for the bottom of the float bowl and I discovered that the exhaust flange that connects the header pipe to the manifold is broken in 2 places 180 degrees from each other. I did pull the AMP meter pick up that was in the connection box and will list it in the used parts thread.
I am sure I will have more questions as I continue to go through the unit but I do want to say a HUGE thanks to all who have helped me get this unit up and working.
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  #70  
Old 04-03-2017, 06:38:03 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Quick help with Onan 12.5

Just curious, where did you find the bad wire/connection to be at?

Very nice that you got it fixed!!!
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  #71  
Old 04-03-2017, 07:28:20 PM
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Default Re: Quick help with Onan 12.5

It was in the control box. I can't remember right now which wire but i guess the mouse pee corroded the crimp on connection. Changed it and got good voltage then it all worked.

Now to get new plugs and set the timming and valves. Then go through the carb again and install the new main jet when i get it.
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  #72  
Old 04-03-2017, 10:50:33 PM
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Default Re: Quick help with Onan 12.5

AND... Keep the MICE out!
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  #73  
Old 04-04-2017, 06:18:44 AM
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Default Re: Quick help with Onan 12.5

I just priced the exhaust flange, $139.61 , Guess I will be making my own. I did just order the main jet, $30 plus $4.39 shipping. I am going to make the exhaust flanges for my 5.0cck so I guess 1 more while I am at it for the JC.
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  #74  
Old 04-07-2017, 08:42:40 PM
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Default Re: Quick help with Onan 12.5

Well, I just discovered another problem, the governor adjusting rod is missing. The spring was still hooked to the rod but not hooked to anything. I guess I will have to pull the blower housing and see if it is laying down in the bottom somewhere. I have been using the throttle stop screw on the carburetor to get the desired RPM. Didn't think it was right but being I have no experience with this model, I didn't know. If need be, is that just a threaded eye bolt?

On a good note, I did get the main jet and got it installed. It starts much easier and no smoke at all on start up. Before it took a lot of cranking and it would then smoke a bit. Funny, seems like one step closer and then one step back.
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  #75  
Old 04-08-2017, 01:54:13 PM
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Default Re: Quick help with Onan 12.5

The things you find in the covers. I pulled the front blower housing off looking to see if the governor mounting stud was in it. To my surprise, i foubd 2 and another spring. Guess they have trouble with these staying put.
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  #76  
Old 04-08-2017, 02:48:45 PM
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Default Re: Quick help with Onan 12.5

The things you find in the covers. I pulled the front blower housing off looking to see if the governor mounting stud was in it. To my surprise, i foubd 2 and another spring. Guess they have trouble with these staying put.
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  #77  
Old 04-08-2017, 04:19:44 PM
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Default Re: Quick help with Onan 12.5

Trying to set the timming, I found 3 marks on the flywheel. Two have yellow paint and the center one does not. When i hook my timming light up to #1 plug, these marks are about 180 degrees away. Is it possible that someone has put the flywheel on 180 degrees off?
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  #78  
Old 04-08-2017, 05:11:30 PM
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Default Re: Quick help with Onan 12.5

I would think that the flywheel end of the crank is keyed. I have a timing light that has a dial on it for retarding the light to Top Dead Center. It displays then how much advance you have. Does your light have such a dial and if so could it not be backed down to ZERO? best way to check the timing marks is to remove all of your spark plugs so you can turn the engine easy. Get a long slim Phillips screw driver. DIS-CONNECT the starting battery and be able to turn the engine by hand. Turn the engine the direction of running and bring the LAST timing mark up to the pointer. That should be top dead center. Insert the screwdriver into the spark plug hole and slowly turn the engine one direction and see if the screw driver moves down into the cylinder OR if you have a good penlight, shine it into the spark plug hole and at top dead center mark, see if the piston is going down. This will tell you if the marks are correct. Are you sure you are using the right stationary mark on the engine?
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  #79  
Old 04-08-2017, 05:33:48 PM
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Default Re: Quick help with Onan 12.5

The flywheel has one keyway and the crankshaft has one key. It can only go on one way. Possibly the marks are for setting valves. Cheers Dan
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  #80  
Old 04-08-2017, 06:04:36 PM
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Default Re: Quick help with Onan 12.5

Where the light blinks, there are no marks on the flywheel i can see. I pulled the distributor cap and when the rotor is firing #1 there are no marks near the pointer. My light is an old non dial style.
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