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Onan 7.5JB FL Spec 306440 Serial 1920484597


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  #1  
Old 04-09-2018, 12:00:06 AM
LMay39168 LMay39168 is offline
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Default Onan 7.5JB FL Spec 306440 Serial 1920484597

Saw this on craigslist a couple weeks ago and in the pictures it looked rough so I decided I wasn't interested at $500. Then I saw where wyM1Aguy had listed the ad on the ebay craigslist forum and yellowlister had commented it was another trifuel extended stack unit. That peaked my intrest and I offered $300 and got no reply for several days and finally he responded and said his bottom dollar was $350. When I got there Friday I was disappointed that there were several parts that were there but not attached to the unit as well as an extra coil, points, plug wires, plugs and other parts that had been changed. So it was apparent it was not running when taken out. Battery was sold in Nov of 02. I started to leave but decided to offer $250 and he took it. Yesterday I filed the points and got the unit to start on propane but it would stop when start switch was released.Found a wiring diagram on the stack ( thanks Billy) and started checking. The start relay had been really messed up. NC contacts were not making etc. Finally figured out it would not actuate when power was applied and found the armature stop was bent and there was to much gap between the armature and the movable arm. Adjusted that and it still would not continue to run when the switch was released. After 2-3 hours of chasing wires I found the diode in the wire from the solenoid to the k12 relay was reversed. Now it runs and generates. The carburetor was really dirty and looked like oil had been leaking on it. When I pulled the air filter off the foam filter was dripping oil, and this had been sitting for several years. I think that created a too rich mixture and that was all that was wrong to begin with and a tech(?) thought he had ignition problems and things went down hill. Thanks to all! Although I don't post much I read a lot and think this site is amazing. I now have collected 3-JC's, 2-JBs, and 1- NHE. Only 1-JC and now 1-JB are running. I've been trying to retire since 65 but maybe now at 71 I'll succeed and have more time to devote to my hobby. I've been in the ac/electrical business and the phone keeps ringing.

---------- Post added at 11:00:06 PM ---------- Previous post was at 10:53:37 PM ----------

By the way. This unit had a point saver on it. It is Onan part number 166-0854
This number has matches on google. They are a little pricey at over $100, but this might help someone.
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Old 04-09-2018, 01:03:54 AM
Ray Lynch Ray Lynch is offline
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Default Re: 7.5JB FL Spec 306440 Serial 1920484597

$250 for a JB and you got it running. That's a good day.
Good luck with it. Gonna hook up to your home?
Ray
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Old 04-09-2018, 07:29:48 AM
Max Thompson Max Thompson is online now
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Default Re: Onan 7.5JB FL Spec 306440 Serial 1920484597

Quote:
Originally Posted by LMay39168 View Post
Thanks to all! Although I don't post much I read a lot and think this site is amazing.

I now have collected 3-JC's, 2-JBs, and 1- NHE. Only 1-JC and now 1-JB are running. .
Sounds like a "closet" addict to me.

The first step to a cure, is admitting you have a problem.
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Old 04-09-2018, 07:42:30 AM
LMay39168 LMay39168 is offline
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Default Re: Onan 7.5JB FL Spec 306440 Serial 1920484597

Not sure if I will use it in my home or use one of the JC's I have. I have natural gas and am not sure if the 7.5 will run my 3.5 ton a/c and other necessary loads. I think my best plan is to temporarily hook up the 7.5 to see if it is adequate. If it will do what I need it surely would be more fuel efficient. I have gas cook top, gas furnace, and gas dryer, so it will probably work. Have a great day. Lee
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Old 04-14-2018, 05:59:50 AM
LMay39168 LMay39168 is offline
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Default Re: Onan 7.5JB FL Spec 306440 Serial 1920484597

I have one problem that I have not researched yet. Maybe someone can save me some time. When I turn the fuel off with the unit running, the k12 relay does not unlatch when the unit stops. I waited 5 minutes thinking the time delay relay should open, but it never did. When the stop switch is actuated the relay opens. What should open the relay in this case or is this normal. Thanks, Lee
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Old 04-14-2018, 10:18:01 AM
nothingbutdarts nothingbutdarts is offline
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Default Re: Onan 7.5JB FL Spec 306440 Serial 1920484597

Shouldn't the contacts in the centrifugal switch open since it's not turning at least 900 RPM, then opening K12 relay?
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Old 04-14-2018, 08:04:12 PM
Max Thompson Max Thompson is online now
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Default Re: Onan 7.5JB FL Spec 306440 Serial 1920484597

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Originally Posted by nothingbutdarts View Post
Shouldn't the contacts in the centrifugal switch open since it's not turning at least 900 RPM, then opening K12 relay?
Yes, the centrifugal switch should kill power to the K-12 relay.

If it is still energized, when the oil pressure goes to 10, it should activate the emergency relay.
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Old 04-15-2018, 12:27:15 PM
LMay39168 LMay39168 is offline
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Default Re: Onan 7.5JB FL Spec 306440 Serial 1920484597

Looking at the wiring diagram the centrifugal switch should kill k12 when the engine stops, but k12 latches when it closes either by manually closing k12 or when closed by s1. The only way to open it is by pushing stop switch. Must be a positive wire hooked to the normally open on k12 that does not belong. Spending time with grand kids now, maybe I can get some hands on time later today and figure this out. Everything works fine now except the relay stays latched when it shuts down for no fuel, also I don't think the low oil pressure switch is working.
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