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Onan 6.5NH-3CE Natural Gas Conversion


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  #1  
Old 01-26-2018, 12:28:47 PM
DrMikeVB DrMikeVB is offline
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Default Onan 6.5NH-3CE Natural Gas Conversion

Hello to all
I am the proud owner of a 1981 Onan 6.5NH-3CE series L Generator. My father gave it to me prior to his passing. It has relatively few hours (sub 500) on it. I have used it as a house back up generator. Where we live we get frequent power outages mostly from pesky hurricanes.
My wife is no longer comfortable with the gas cans all around when we have to put it into use. She also has been pushing to get a new generator from the one of the big box stores. The good news is we have natural gas at the house.
My question is has anyone done more of a DIY natural gas conversion? Meaning using a demand regulator with some type of piping configuration to carry the nat gas into the air cleaner side of the carb. I have been in contact with US Carb and Nash Fuels but neither seem to have the exact adapter that will fit my application.
The carb has a fitting on it to accept a 1 1/2 inch hose for the air cleaner. Is there any reason why I could not simply bore a hole into the air cleaner hose and put a brass fitting thru it to supply the nat gas to the carb? If so what size I.D. fitting would be required to allow enough gas for the generator to run at full load?
Thank you in advance for your assistance.
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Old 01-26-2018, 12:33:59 PM
nothingbutdarts nothingbutdarts is online now
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Default Re: Onan 6.5NH-3CE Natural Gas Conversion

Just a FYI, you will maybe loose 500 watts going from gasoline to propane fuel.
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Old 01-26-2018, 12:44:16 PM
JT240Z JT240Z is offline
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Default Re: Onan 6.5NH-3CE Natural Gas Conversion

One problem I see with that approach would be a lack of mixture control. How would you tune the carb for proper air/fuel mixture?
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Old 01-26-2018, 01:18:28 PM
Kevin K Kevin K is offline
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Default Re: Onan 6.5NH-3CE Natural Gas Conversion

Plenty of people here have converted to propane. The procedure for converting to natural gas would be the same. Do a search here on the forum for propane conversions. Here is one such thread: https://www.smokstak.com/forum/showthread.php?t=158410

You will need to purchase a Garretson demand regulator and modify the carburetor to put the stub down in the carburetor venturi. You cannot put the gas supply stub in the air hose.

Expect to lose maybe 20% of the power generating capability when running on natural gas.

Go here: http://onan.xmsi.net/

Download the manuals for your generator and the T-015 gaseous fuels manual.
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Old 01-26-2018, 01:19:30 PM
Mac Sine Mac Sine is offline
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Default Re: Onan 6.5NH-3CE Natural Gas Conversion

A properly-adjusted demand regulator requires a vacuum signal derived in the carburetor venturi to allow the regulator to admit fuel to the carburetor. A "carburetor adaptor" adds a gas mixing venturi between the gasoline carburetor and the air filter.

Another approach for a gas-only system is to replace the gasoline main jet in the original carburetor with a larger jet sized to handle a gaseous fuel. In this way, the original venturi is used to derive the signal needed by the demand regulator. This type of modification is not always feasible; the material surrounding the original gasoline jet may not be large enough to allow enlargement to accommodate a gaseous fuel jet.

Contact Phil or Eric at Carburetion and Turbo Systems, Inc. in Shakopee, Mn., and ask if they can help you locate equipment you need. I think they will be able to help you. (952) 445-3910.

As noted by others, you will need a load block, for air/fuel mixture adjustment, between the demand regulator and the carburetor. You may also need a positive fuel lock, depending on how you are installing the generator. Although a demand regulator will stop the flow of fuel gas when there is no vacuum signal, regulatory authorities do not consider a demand regulator to be a "positive shut-off". Check with your local codes if you are making a "permanent" installation.
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Old 01-28-2018, 11:12:18 AM
DrMikeVB DrMikeVB is offline
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Default Re: Onan 6.5NH-3CE Natural Gas Conversion

Attached is photos of the carb setup I have. As you see in the one photo there is a flange that the air cleaner hose attaches to. Would it be possible to Simply tap A fitting on to the top of that flange to feed the gas into the carburetor? If so what would the ID of the fitting need to be? It seems to me that the better place for the adapter would be between the carburetor and the engine intake . That way the choke would be effective at startup. If I fed the gas up through the bottom of the carburetor how large would I need to drill it out?
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Old 01-28-2018, 12:05:10 PM
nothingbutdarts nothingbutdarts is online now
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Default Re: Onan 6.5NH-3CE Natural Gas Conversion

I bought a 6.5 already converted a few years ago. I tried to attach pictures but, it will not let me attach them. I believe I have already posted them here however I can't find them. I think the sight will only let you post a picture one time. I could e-mail them to you if you would like. It was done by an adapter screwed onto the inlet side of the carb.
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Old 01-28-2018, 12:20:51 PM
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Jim McIntyre Jim McIntyre is offline
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Default Re: Onan 6.5NH-3CE Natural Gas Conversion

There's a fundamental principle of gaseous carbs that needs to be made crystal clear before proceeding. Maybe you know this already, so don't take offense if it was obvious.

The fuel gas needs to be fed into the carb in the venturi. The reason for this is that in the venturi, the pressure is inversely related to the air flow. As the carb butterfly opens and allows more air flows into the engine, the pressure in the venturi drops, and this is the key action that draws in more fuel. It's amazingly simple, and works amazingly well, but requires two basic things:

Thing 1 - fuel gas needs to enter the venturi
Thing 2 - fuel gas needs to be supplied by a 'zero pressure' regulator.

So the simple approach is something along these lines:



(Note that the first 'butterfly' you see is the choke plate, which needs to be 100% open for gaseous carburation) This works, but of course you'll need to tinker at the detail for your particular installation...

I have completed numerous DIY natural gas conversions on little gensets, so ask away...


https://www.smokstak.com/forum/showthread.php?t=113911

https://www.smokstak.com/forum/showthread.php?t=144397
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Old 01-28-2018, 12:26:26 PM
reid070 reid070 is offline
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Default Re: Onan 6.5NH-3CE Natural Gas Conversion

The link in post 4 from Kevin K ,has a good diy solution for you. It will also leave the generator able to run on gasoline.

Steve
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Old 01-28-2018, 07:46:28 PM
nothingbutdarts nothingbutdarts is online now
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Default Re: Onan 6.5NH-3CE Natural Gas Conversion

See post # 41 here for the NH I bought that had the adapter:

https://www.smokstak.com/forum/showt...=173642&page=3

And THANK YOU to the guys here for telling me how to find my posted pictures!
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