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Possible new toy Onan 7.5 JB


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  #11  
Old 02-13-2017, 12:53:40 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Possible new toy Onan 7.5 JB

Would there be a chance that when running NG it might not have full output unless it had the high compression pistons? Which it must no being a tri-fuel unit.
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Old 02-13-2017, 01:19:50 PM
Leon N. Leon N. is offline
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Default Re: Possible new toy Onan 7.5 JB

The C1 comb carb connotes a tri-fueled carburetor. That is exactly what I have on my JB. The Onan owners manual, 967-320 cautions that when burning natural gas, the output is reduced 20% due to the lower heat content of the ng as compared to running on gasoline or propane.

Now my experience with the low compression JB is that I can easily achieve the full output, 7.3 KW/31 amps with ng. I have measured the compression and recorded 90 psig and my owners manual states the compression ratio is 6.5:1.

I have concluded that these early build Onans were designed with at least a 20 % reserve power to handle any unintended over loads or abuse. Friends, they don't build them like that any more. In fact, I suspect my magneciter, 04SX1N3B is good for 10 Kw! Somewhere I recall noting the 10Kw version uses the same magneciter. Will research this again to verify.
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Old 02-13-2017, 01:48:37 PM
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Motorhead Motorhead is offline
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Default Re: Possible new toy Onan 7.5 JB

My YD end later JB has the tri fuel carburetor and standard compression also. I can pull 30 amps a side on mine with no issues. It also has close to the starting reserve that Leon's set has.
The main importance with running natural gas is having extra supply capacity (ample pipe diameter) so the engine has what it needs for any surges in demand.
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Old 02-13-2017, 05:42:00 PM
squidtrap squidtrap is offline
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Default Re: Possible new toy Onan 7.5 JB

So, i just finally talked to the sellers father. It has not run in 3 years, they pulled it from a stop and shop, was used for back up.

No gas train, he does not know about the rubber feet, and knows nothing about the gen.

I asked him to take a pic inside the control box explaining the mice damage he said he would tomorrow. Does not seem to motivated, takes a day or so for any reply.

I explained the deal of a 50YO cold hunk of steel and he basically understood, but who knows, will wait on pics of control box, Ed
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Old 02-13-2017, 06:32:01 PM
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Default Re: Possible new toy Onan 7.5 JB

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Originally Posted by squidtrap View Post
So, i just finally talked to the sellers father. It has not run in 3 years, they pulled it from a stop and shop, was used for back up.

No gas train, he does not know about the rubber feet, and knows nothing about the gen.

I asked him to take a pic inside the control box explaining the mice damage he said he would tomorrow. Does not seem to motivated, takes a day or so for any reply.

I explained the deal of a 50YO cold hunk of steel and he basically understood, but who knows, will wait on pics of control box, Ed
Give him a low offer with the statement, "I could be buying a RUNNER or I could be buying a BOAT ANCHOR. This is the amount I am willing to GAMBLE with". I give them the facts about how much could be wrong with a 50 year old machine and part availability. I also say, "I'm here right NOW with money in hand". Chris
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Old 02-13-2017, 06:36:21 PM
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Default Re: Possible new toy Onan 7.5 JB

If the seller knows nothing about the generator, I would be very hesitant asking him to open the control box. He may end up doing damage. If the seller is not too far away, I'd go visit him with a bunch of $10 bills in your wallet. Any damages found by you would mean less $10 bills I'd pull out of my wallet, but a bunch of $10 bills looks more impressive than a couple of $50 bills.

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Old 02-13-2017, 07:51:29 PM
squidtrap squidtrap is offline
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Default Re: Possible new toy Onan 7.5 JB

JohnnyC/Motorhead- prob. i have is im dealing w/2 people. the son- by e-mail, father only 1 time on phone after 3 calls.

The father filled my bag about the missing items, thats when i explained the boat anchor runner situation to him. Told him after pic of control box i would still possibly like to see it.

Yes, there is not going to be to many 50's or 100's in pocket, but i do believe its a runner cause it was a stop/shop pull out. they took pick to the effect, property of s/s (think they went out of business)

Anyhow just e-mailed son and informed him of conversation w/ father so he might snap pic quicker, he did w/data plate. Just a waiting game now.
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Old 02-13-2017, 08:38:23 PM
Ray Lynch Ray Lynch is offline
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Default Re: Possible new toy Onan 7.5 JB

Heh Leon
Is your lifting bracket held to the valve cover with 1 bolt or 3?
My 1965 JB has a bracket that looks like yours with 1 large bolt only holding it to the valve cover.
My 1985 JB has a bracket with 1 large bolt threaded into the valve cover and 2 holes that accept 2 valve cover bolts as well.
Both brackets are oriented with the angle legs parallel to the sets length.
Ed..may want to eyeball that bracket before lifting to check if its attached to your liking.
I chased the guy back and forth almost a month before buying my 2nd JB.
Don't be shy about starting low and working up to your top offer.
From what you describe, sounds like your in a good bargaining position.
Good luck.
Ray
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Old 02-13-2017, 09:26:54 PM
JohnnyC JohnnyC is offline
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Default Re: Possible new toy Onan 7.5 JB

My JB's list bracket (see picture below).

JohnnyC
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Old 02-13-2017, 09:38:41 PM
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Jim McIntyre Jim McIntyre is offline
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Default Re: Possible new toy Onan 7.5 JB

Quote:
Originally Posted by nothingbutdarts View Post
Would there be a chance that when running NG it might not have full output unless it had the high compression pistons? Which it must no being a tri-fuel unit.
Yes. There's a chance. Basically, from what I've seen on numerous JB and CCK sets, pretty much all of the engine's 'reserve' power that is present with gasoline goes away with natural gas. I see JB's make 10 kW on gasoline, but they max out at about 7.5 kW on natural gas. And I know they had sufficient gas supply, optimum mixture and timing.

This had to be why Onan made the high-compression variants in the first place.

Obviously, the max power a guy gets depends on the BTU value of the natural gas. It runs pretty close to 1000 BTU/cu foot here. I think this is 'typical'.
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