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Quick help with Onan 12.5


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  #41  
Old 03-14-2017, 06:35:25 AM
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Default Re: Quick help with Onan 12.5

Gaseous regulator question, according to the parts book, I need a 148-0311 low pressure regulator for gaseous fuel. I can't believe the price differences around for the same regulator. I have found from $78 to over $300 Are these all the same just some folks want to retire early?
Is this the only thing I need to run this on natural gas? It is all the parts book shows but I don't know much about dual fuel set ups.
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Old 03-14-2017, 06:40:37 AM
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Default Re: Quick help with Onan 12.5

I have not found an after market filter that fit right yet. The OEM filters are in the $23 range, but should last many years. They are foam and can be washed out and reused.
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  #43  
Old 03-14-2017, 11:58:06 AM
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Default Re: Quick help with Onan 12.5

That regulator is what is known as a demand regulator which stops the fuel flow when the engine is not turning over. When the engine is cranking or running it generates a small amount of vacuum in the manifold connected to the regulator. This causes the reg to open up and fuel to flow into the engine. The $78 ones are pretty much the same as the $300 ones except for where they are made. You need the reg and a 12V fuel solenoid to safely run the engine. Cheers Dan
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  #44  
Old 03-18-2017, 02:58:09 PM
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Default Re: Quick help with Onan 12.5

I am so close! I got a muffler on her today and the oil changed. Fuel pump working.
I now can hit the start switch and it gets running but as soon as I let go of the switch, it just dies. What do I need to look at? I have tried the points in the cover off the blower housing, held them open then tried holding closed, no luck. Any help appreciated!
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Old 03-18-2017, 03:29:50 PM
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Default Re: Quick help with Onan 12.5

The "points off the housing" I assume are the centrifugal switch under the domed cover by the oil filter. You are on the right track, are they making contact when you hold them closed? They may be dirty. When the centrifugal switch closes, it powers the K-12 relay in the control box to provide ignition power & disconnect the starter. The K-12 relay has 2 sets of points also that must "make contact" in order to keep the set running after you release the start switch.

All the above is covered in the service manual.

I just bought a KN demand regulator from Century Fuel Products for around $40. It seems to be a good product. Also bought a couple 3/4" 12-V Asco solenoid valves for $49 ea. Asco valves have been around for a long time and are a very good valve.
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  #46  
Old 03-18-2017, 03:36:51 PM
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Default Re: Quick help with Onan 12.5

Do you have along with the OIL PRESSURE GAUGE an OIL PRESSURE SWITCH? Does your unit have the LOPKO red reset button? If you have the oil pressure switch, disconnect the single wire to it and see if the set will run after starting. Remember, you have to hold the start switch until the engine comes up to speed and the start disconnect cuts in. My JB did the same "No run" after letting off of the start button. Turns out my oil pressure switch was bad and wouldn't open under oil pressure.
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  #47  
Old 03-18-2017, 03:56:47 PM
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Default Re: Quick help with Onan 12.5

So I have it running but I have to hold the points closed on the switch in the control box. I think they called it a latch in switch? If I close those it purrs like a kitten.
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Old 03-18-2017, 04:15:12 PM
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Default Re: Quick help with Onan 12.5

How bout a picture of the "points" in the control box you are holding closed?
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Old 03-18-2017, 05:00:14 PM
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Default Re: Quick help with Onan 12.5

It appears to be ignition relay according to the schematic. It is actually in rough shape. I will need to get a new one and then also do some voltage checks to see if it is getting the voltage to close or not.

I did check the oil pressure switch, it is okay.
I do have voltage at the points in the bell cover at the front of the engine.

I am about done for today though.
Here is what I found out today.
1- the engine does run and seems to run well. No funny noises and smooth.
2- it does produce AC voltage, right at 120 on my fluke.
3- it does produce 12 volts to charge the battery. I did not get an actually reading but the amp gauge does work and was showing charging.
4- it has really good oil pressure, so good I will have to take out the 15w40 I put in and drop to a 10w30. It pegs the gauge now.

Bad
I need the ignition relay and still some other work to do. Definitely getting closer though. 😊
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  #50  
Old 03-18-2017, 07:55:47 PM
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Default Re: Quick help with Onan 12.5

Here is the part I will need to find and trouble shoot. In the second picture, the yellow pencil is where the points are that I have to close to make it run.
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