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Onan 15 OJC-3CR NG to Gasoline Carb Conversion


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  #1  
Old 11-27-2010, 09:53:19 PM
BallyOnan BallyOnan is offline
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Default Onan 15 OJC-3CR NG to Gasoline Carb Conversion

I have a recent purchase Onan 15KW Genset from the 70's. It ran on NG as a backup generator in its prior life. I would like to run it on gasoline because I only need power periodically to run large power tools in the barn. A large enough LPG tank would be impractical. The manual implies that this gen could run on either gasoline or gas and the carb looked normal on the outside but.... No float, float axle, needle, seat, jet, jet adjust, choke. Anyone know if parts or a suitable replacement carb is available? I attached ID and carb photo. Numbers stamped on top of the Zenith carb are 13283 and 141D725. Thanks!
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  #2  
Old 11-28-2010, 03:57:18 AM
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lokay5 lokay5 is offline
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Default Re: Onan 15 OJC-3CR NG to Gasoline Carb Conversion

From my limited experience with Zenith gaseous carburetors, many gaseous carbs built with a float bowl, can be easily converted to gasoline by installing the missing gasoline internals. The carburetor will then work with both gasoline and gaseous fuels. You will then have a tri-fuel carburetor, a very desireable unit. Obtain a gasoline Zenith that has the same body (they're pretty common) and transfer the float, needle/seat, main jet etc. The choke will also fit. You just have to knock out the plugs for the shaft. All the passages for gasoline are (probably) in your gaseous carburetor body.
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Old 11-28-2010, 04:45:55 AM
Old Style Old Style is offline
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Default Re: Onan 15 OJC-3CR NG to Gasoline Carb Conversion

Two things to consider are that some gaseous JC's are high compression. Mine is a 1978 and has 220lbs per cyl. Much to high, I think, for gasoline. I don't know how many are that way but you might want to take a compression test to know before changing.

The other is usage. If you are only going to use "periodically to run large power tools in the barn." you won't need a huge tank. Gasoline goes bad so quickly these days and LPG never goes bad. A couple of forklift style "Vapor" tanks might work for you; even if you used a couple of gal's an hour.

Just my two cents....
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Old 11-28-2010, 08:35:38 AM
BallyOnan BallyOnan is offline
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Default Re: Onan 15 OJC-3CR NG to Gasoline Carb Conversion

Good points. I'll check the compression; I may have to use higher octane fuel to avoid pinging. I thought about the liquid-tank LP operation and am still on the fence. I assumed I would have to install an electric vaporizer(if they make those?) because this is an air-cooled motor so there is no source of hot water like on a fork lift. I would also need a pressure regulator. The engineering on this is unfamiliar to me. I'm guessing the motor is around 25-30hp range. Old fashioned gasoline is more in my comfort zone. I'll check the forum for more info; any favorite links to similar conversions would be much appreciated.
I'll also troll around the web for a similar carb but I am not too hopeful there; very difficult and risky purchase on the internet.
The good news here is that the motor started right up and sounded good on starting fluid so a bit more expense is warranted.
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Old 11-28-2010, 09:48:53 AM
Gunny Gunny is offline
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Default Re: Onan 15 OJC-3CR NG to Gasoline Carb Conversion

Gasoline is about the last in choice of fuels.

Get with these folks for any of your dry fuel needs or questions. The best in the business.

http://www.mouldensupply.com/

Yes, there are vaporizers for air cooled engines.
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Old 11-28-2010, 11:41:39 AM
bobbyz72 bobbyz72 is offline
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Default Re: Onan 15 OJC-3CR NG to Gasoline Carb Conversion

When i got my JB 7.5, it too was missing a couple parts in the carb, the float and needle. It was only run on natural gas, when I put regular gas in it, it sounded really bad, then i tryed avation gas 100LL in it... purrrs like a kitten. From what ive read, ava does not go bad for years if stored properly. Its all ive been using in my generators, fourwheelers, lawnmowers etc...
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Old 11-28-2010, 01:25:28 PM
MBB MBB is offline
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Default Re: Onan 15 OJC-3CR NG to Gasoline Carb Conversion

Aviatiojn fuel very high octane. Especially made for high compression.
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