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Onan Generators

ONAN JB 7.5 new life


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  #21  
Old 03-10-2017, 04:09:51 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

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Originally Posted by Leon N. View Post
I went out and took a picture of my JB fuel pump to see if it was leaking oil. Guess not. JB has been in operation since 1970. You may want to think twice about using an electric fuel pump WRT the mean time between failure (MTBF). Obviously you would want a high quality device.
It may not be leaking, but it sure looks like the bolt is loose. Maybe not.
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  #22  
Old 03-10-2017, 04:12:37 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

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Originally Posted by HBSaunders View Post
was about to bid on that one but was hoping to come up with a decent diesel, keeping my eyes open for one closer to home,howard
I'm glad you didn't. Hope you find you a good diesel.
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  #23  
Old 03-10-2017, 04:49:04 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

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Originally Posted by Max Thompson View Post
That is a pin that the pump pivots on. I have had "some" luck using a punch to expand the ends of the pin to stop the leak. My preferred option is to block off the mech. fuel pump and add an electric fuel pump.
I found a cut away of a smilar pump. The pin I have marked with an arrow, if I see it correctly. Is that pin just pressed in there and over a lot of usage works its self loose. I guess is its suppose to be stationary or TIGHT.
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  #24  
Old 03-10-2017, 05:24:22 PM
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Default Re: ONAN JB 7.5 new life

I would Check the operation of the crankcase breather. Could possibly be partly plugged or inoperable causing excessive crankcase pressure forcing oil out of the fuel pump pin. Some sets that have seen gaseous fuel service will accumulate sludge around the check valve causing it to stick.
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  #25  
Old 03-10-2017, 05:28:09 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

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Originally Posted by BRae View Post
I would Check the operation of the crankcase breather. Could possibly be partly plugged or inoperable causing excessive crankcase pressure forcing oil out of the fuel pump pin. Some sets that have seen gaseous fuel service will accumulate sludge around the check valve causing it to stick.
Thank you. I was planning on checking that just hadn't got around to it.I'll check it right now.
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  #26  
Old 03-10-2017, 07:38:58 PM
Max Thompson Max Thompson is offline
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Default Re: ONAN JB 7.5 new life

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Originally Posted by fisherman81654 View Post
I found a cut away of a smilar pump. The pin I have marked with an arrow, if I see it correctly. Is that pin just pressed in there and over a lot of usage works its self loose. I guess is its suppose to be stationary or TIGHT.
Yes, the pump arm pivots on this pin.
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  #27  
Old 03-10-2017, 08:42:18 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

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Originally Posted by BRae View Post
I would Check the operation of the crankcase breather. Could possibly be partly plugged or inoperable causing excessive crankcase pressure forcing oil out of the fuel pump pin. Some sets that have seen gaseous fuel service will accumulate sludge around the check valve causing it to stick.
The inside of the crankcase breather looks new.
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  #28  
Old 03-10-2017, 09:05:27 PM
Ray Lynch Ray Lynch is offline
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Default Re: ONAN JB 7.5 new life

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Last edited by Ray Lynch; 03-10-2017 at 10:36:38 PM.
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  #29  
Old 03-11-2017, 01:25:06 PM
Leon N. Leon N. is offline
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Default Re: ONAN JB 7.5 new life

Fisherman I checked that fuel pump bolt and it is not loose as you thought in post 21
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  #30  
Old 03-13-2017, 07:20:58 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

I had to order a new valve pan gasket and it came in today.
I installed the gasket and started it up and run fine.
Ok I put a inline filter before the bowl filter just to keep it from getting dirty.
Started it up, NOT. It would not start. After quite a few attempts it got fuel to the new filter. Still would not run. Took the bowl off the carburetor and cranked it, gas came out in bowl area. Put it back together and still the same problem. Checked plugs, nice blue arc on both and both had no fuel on them.

I tried starting fluid and that seem to flood it out.
When I crank the engine over it try's to run but dies out as soon as you release the start button. Also during this process I have to manually hold the choke throttle open or it wont hit at all.

Makes no sense, all I did was add a filter and later I took the filter out that I added, no luck. Fuel pump suddenly not enough pressure? A relay suddenly fail? A air lock? I don't know.
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