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Old 04-10-2014, 14:52   #1
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Propane vs. Butane in a Lehr propane outboard

I was talking to a friend of mine at the yacht club, John Prentice (formerly of SCARLET O'HARA), who, with his wife Renee, cruised extensively in the Western Pacific. He remarked that, in a number of places, butane was more common than propane as an lpg fuel. I am curious as to the suitability of butane for use in a Lehr propane outboard. I know that butane has a higher calorific value per volume, and burns hotter than propane, but that the regulator (blue for butane, red for propane) usually takes care of this issue. Aside from the issue of being able to actually fill my horizontal aluminum tanks for the stove propane and filling the horizontal liquid composite tanks for the outboard supply, I'm wondering if there is any issue with using butane in place of propane for the outboard. Can anyone address this? It may be a moot question since I have no plans for cruising Indonesia, but I'm curious, anyway.
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Old 04-10-2014, 15:05   #2
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Re: Propane vs. Butane in a Lehr propane outboard

Simple - Contact the manufacturer of the motor. Ask them if it can be converted to run on butane. They will answer your question and then you will know for sure.
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Old 04-10-2014, 16:16   #3
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Re: Propane vs. Butane in a Lehr propane outboard

Lehr will tell you that in theory you can do it, but you'd need to adjust the mixture. Or that is what they were telling people a year ago.

Given the fact that butane is sold in place of propane in many parts of the world, I'm sure they've investigated this by now if they want to expand into europe, for example.
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Old 07-10-2014, 09:46   #4
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Re: Propane vs. Butane in a Lehr propane outboard

Here's what Elton Barker at Lehr (Eiton Barker <customersupport@golehr.com)has told me:

This has actually come up quite a bit as our motors have been making there way across the globe. I unfortunately do not have a definite answer for you yet since we have not done any testing with butane at this point, but from talking to our engineering department they are pretty sure our motors will run on butane but adjustments will definitely need to be made and you will not get peak power or efficiency out of the motor. Our motors have been specifically designed to run on propane and propane of 90% grade or higher so we cannot officially guarantee our motors functionality on butane but are confident after some work is done they will to a certain point.

Please keep in mind that our 15HP needs to run on liquid propane not vapor. This only has to deal with the tank itself not when it is filled. The tank will turn vapor propane into liquid so you don't have to worry about finding propane already in liquid form. I am sorry I cannot give you a definite answer but its all I have for you at this point.

Please let me know if you have anymore questions or concern's I'd be happy to help.

I'm happy with that, especially since I will probably only end up in propane places.
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Old 07-10-2014, 10:33   #5
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Re: Propane vs. Butane in a Lehr propane outboard

" needs to run on liquid propane not vapor " ?? Say what ?? Propane is sold by liquid weight, and vaporizes at around 100-125 psi.

Does the Lehr have a sealed fuel injection system with pump, like a diesel ?
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Old 07-10-2014, 11:05   #6
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Re: Propane vs. Butane in a Lehr propane outboard

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Does the Lehr have a sealed fuel injection system with pump, like a diesel ?
Nope - they've got carbs. There's a regulator integral to the carb. I'm guessing that the requirement for liquid fuel on the 15hp is just to get enough fuel to the carb - i.e. volume of liquid vs gas. The smaller motors run fine on gas. (I'd also guess that the carb on the 15 is designed to stay warm, because all that propane tuning into gas is gonna make lots of cold) - The 2.5hp that I have deals with that by letting engine heat warm up the disposable bottle a bit.
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Old 07-10-2014, 11:15   #7
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Re: Propane vs. Butane in a Lehr propane outboard

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Nope - they've got carbs. There's a regulator integral to the carb. I'm guessing that the requirement for liquid fuel on the 15hp is just to get enough fuel to the carb - i.e. volume of liquid vs gas. The smaller motors run fine on gas. (I'd also guess that the carb on the 15 is designed to stay warm, because all that propane tuning into gas is gonna make lots of cold) - The 2.5hp that I have deals with that by letting engine heat warm up the disposable bottle a bit.
In the meantime I viewed Lehr's site. Functions as I thought. IMO, not a well worded answer from Lehr. Worked on lots of LPG-fueled forklifts, so well familiar with systems.
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Old 07-10-2014, 11:15   #8
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Re: Propane vs. Butane in a Lehr propane outboard

I don't know about a Lehr, but I do about fork lifts and automotive conversions, etc. Not sure I would call it a carburetor, but it does serve that function.

I've wondered why some that seem to want a propane powered outboard don't simply convert their Honda or other four stroke to propane? Myself I'd rather have the Honda, especially if I already had it.
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Old 07-10-2014, 11:49   #9
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Re: Propane vs. Butane in a Lehr propane outboard

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............ I've wondered why some that seem to want a propane powered outboard don't simply convert their Honda or other four stroke to propane? Myself I'd rather have the Honda, especially if I already had it.
OK, can you tell us how to do that?
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Old 07-10-2014, 12:53   #10
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Re: Propane vs. Butane in a Lehr propane outboard

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I don't know about a Lehr, but I do about fork lifts and automotive conversions, etc. Not sure I would call it a carburetor, but it does serve that function.
Lehr calls it a carburetor in their documents, hence my calling it a carb.

I guess it's more of a throttle-body injector sort of dealio tho, as the fuel is pressurized vs extracted by venturi.

Got mine used, only about half-happy with it so far. I don't think I'd recommend one for long-distance cruising.
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Old 07-10-2014, 12:57   #11
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Re: Propane vs. Butane in a Lehr propane outboard

Those vertically suspended 1lb disposable cylinders convey propane vapor to a BBQ by the natural conversion of liquid - to- vapor pressure formed above the liquid. How does a liquid get to the gas-expansion regulator once the liquid (nominally 1/2 full) falls below the exit fitting on the cylinder.
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Old 07-10-2014, 15:02   #12
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Re: Propane vs. Butane in a Lehr propane outboard

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OK, can you tell us how to do that?

There are dozens of kits to convert everything from lawnmowers, small generators to even engine driven floor polishers to propane, I'd install one of those kits, and unless I'm wrong you retain the ability to burn gasoline.
Just google small engine propane conversion or similar. Common in the RV world to see one of the little generators like the Honda running off of a 20 lb gas grill bottle.
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Old 07-10-2014, 15:22   #13
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Re: Propane vs. Butane in a Lehr propane outboard

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There are dozens of kits to convert everything from lawnmowers, small generators to even engine driven floor polishers to propane, I'd install one of those kits, and unless I'm wrong you retain the ability to burn gasoline.
Just google small engine propane conversion or similar. Common in the RV world to see one of the little generators like the Honda running off of a 20 lb gas grill bottle.
I've seen the kit for the generator and it seems like a pretty good idea, especially if you don't use it a lot. I've never seen one for an outboard motor though.
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Old 07-10-2014, 15:29   #14
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Re: Propane vs. Butane in a Lehr propane outboard

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I've seen the kit for the generator and it seems like a pretty good idea, especially if you don't use it a lot. I've never seen one for an outboard motor though.

The kits cover a pretty wide range of engine displacement / HP, I have never installed one, but what is special about an outboard?
Gotta be a reason or you would surely have seen them?
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Old 07-10-2014, 15:35   #15
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Re: Propane vs. Butane in a Lehr propane outboard

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Those vertically suspended 1lb disposable cylinders convey propane vapor to a BBQ by the natural conversion of liquid - to- vapor pressure formed above the liquid. How does a liquid get to the gas-expansion regulator once the liquid (nominally 1/2 full) falls below the exit fitting on the cylinder.
In the case of the lehr, you use a propane cylinder that draws the liquid out - from the bottom.

Only the 2.5hp and 5hp versions can run with the 1lb bottles. The 9.9 and 15 need a bigger tank.

If I think about it, my 2.5 may run on liquid sometimes, because the bottle is horizontal, and I assume that a full 1lb bottle is more than half full.
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