Yamaha outboard conversion to LPG

Discussion in 'Outboards' started by sailor305, May 23, 2012.

  1. Petros
    Joined: Oct 2007
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    Petros Senior Member

    Clairification: the lower the pressure across the new propane jet, in the throat of the carb, the more the diaphame opens the needle valve to allow more fuel to flow into the jet.

    The fuel supply is regulated by the pressure in the fuel supply manifold (or tube), not the intake manifold of the engine.

    This particluar kit sacrifices the gasoline carb to make it run on propane only. They had other, much more costly kits, if you wanted to keep the gasoline fuel supply as an option.

    Since the carb was already junk, and I see no reason ever to use it with gasoline again, I choose the less costly kit. And if I ever wanted to run it on gasoline I would need a new carb anyway, and it only takes a few min to swap the carb anyway.
     
  2. jonr
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    jonr Senior Member

    AFAIK, all carburetors work by using a venturi. More flow causes more vacuum which causes more fuel flow. You wouldn't want to use manifold vacuum to draw in fuel - that is high at idle and low at full throttle (the reverse of what you want).
     
  3. mariocroatia
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    mariocroatia Junior Member


    a 9lb tank or maybe u think 90 lb tank
     
  4. shameer
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    shameer New Member

    Hai All
    My name shameer From kerala (India).I want to inform you that Surya Marine LPG Kit help you to convert your outboard engine to LPG.This company giving Gas Convertion kit to 9.9HP,25HP nad 40HP Engines.If you required more details about our company product please give request to my mail ID .shameerts2009atgmaildotcom.Now this company going to start kerala operation.Then spreading world wide.This is the first company started LPG Marine kit with Certifications
     
  5. Barry
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    Barry Senior Member

    There are many propane tanks that are set up for horizontal mounting, such as forklift truck bottles as the most common. They will have an indexing tab on the handle to properly
    locate the tank in the proper location to ensure that you will not get liquid into the fuel line.

    Would there be a possibility for liquid propane to reach the outlet in heavy seas or would you expect that the vapor volume above the liquid in the tank would be enough of a
    distance to make this an improbability?
     
  6. rwatson
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    rwatson Senior Member

    I would have trouble thinking of as good reason to use Propane. It only has half the energy of the equivalent amount of petrol.
     
  7. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Lehr and Tohatsu make them now and up to 25 hp.
    Evidently they burn cleaner and perhaps there other advantages like a completely non vented method of carrying fuel around.
     
  8. Dave T
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    Dave T Senior Member

    LP gas will give you about 90% of the power of gasoline. It is very simple to convert any small HP 4 cycle motor to run on propane. The main thing you have to have is a regulator that doesn't flow any gas unless there is vacuum from the motor these are available from US carburetion for about $70.00. Google gas to LP conversion kits. I have converted my generator to run on LP. You don't need to make any changes to the carburetor you just need run a small tube into an adapter between the air cleaner and the carburetor. The the motor can run on either gasoline or LP. The biggest disadvantage for doing this on a boat motor would be the weight of the tank needed and no gas available at most mariners and also the cost of having tanks filled unless you can do it your self. I have liquid fill hose on my 500 gallon LP tank and fill all of my own small LP tanks. LP weighs about 5 lbs per gallon but a 30 lb LP tank weighs about 60 lbs when full and holds about 6 gallons of LP. I wish I could run my 70 HP outboard on LP but it's a 2 cycle I can buy LP for about $1.25 a gallon right now and sometimes during the Summer for about $1.00 where gas with out alcohol which is getting harder to find is about $3.50 at a station and as high as $5.00 on the river. Here is a pic of my generator converted to run on LP or gasoline. 100_1223.JPG
     
  9. fallguy
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    fallguy Senior Member

    LP is lousy here in frigid Minnesota.

    Guy that shrink wraps my boats heats the bottle with his flamethrower.

    I watched my 1#propane stove bottle freeze one day out camping and the cooker simmered my breakfast.

    No thanks. Not here anyhow.
     
  10. Dave T
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    Dave T Senior Member

    LP is not a real problem in cold weather but the smaller the tank you use the less you can use out of it and the less you can flow from it. I've run my generator down to 10 degrees F. but on a 20 lb tank you can only run about a half a tank before the pressure drops low enough not to run. It's not a problem when running off of a 500 gallon tank. If you research it will tell you how long you can run at different temperatures with different size tanks at different horse powers. I definitely recommend if you have a generator for emergency power you convert it to LP or natural gas. Most times when the power is off for a long time you won't be able to get gasoline and you can't store gasoline for very long. LP can be stored for at least 20 years without any problem. The problem with your small tank was most likely that it was low on gas to start with and the tank wasn't large enough for as cold as it was. They also make electric heaters for small LP tanks.
     
  11. fallguy
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    fallguy Senior Member

    New full tank. It was colldd.
     
  12. Dave T
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    Dave T Senior Member

    This is not relevant to the OP's thread as he wants to run an outboard on LP so I don't think he will be running it below 32 degrees F. and probably only when its hot so he would be smart to have a tank with an OPD because if the tank is overfilled they will vent off gas if they get too hot.
     
  13. fallguy
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    fallguy Senior Member

    Look, my experiences are above freezing or I would have not commented. The tank freezes due to the nature of propane; not freezing temps.

    Honestly, cool weather and propane are a concern.

    I like the idea of alt fuels, but propane is no panacea as it is also subject to price swings; especially here.
     
    Last edited: May 29, 2018
  14. rwatson
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    rwatson Senior Member

    Propane is less than 90% of petrol power, down around 75%, unless you have a gas injector system, which actually performs better than petrol.

    I run a V6 utility vehicle on Propane, and here in Australia we pay around $au.95 cents a litre (US4.80 a gallon) , so that's about $US5.00 a gallon too.

    Since petrol is about $us7.40 a gallon in Australia, its a bit cheaper, if I switch to Petrol for hill climbing and loads.

    For continuous usage in a boat engine, I bet the Propane power would be below 70% to Petrol, as it would be under continuous load.

    I dont understand your freezing concerns
    " What many want to know is if the propane tank ever gets too cold to work.
    The average winter temperature at the South Pole is about -56.2°F (-49°C).
    So, if you live in Antarctica, your LPG (propane) could stop functioning if the temperature dropped below -43.6°F (-42°C), the boiling point of propane."
     

  15. Dave T
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    Dave T Senior Member

    The only way you can save money using propane is if you can fill your own tanks with gas that is bought for home heating as you are not paying road taxes. This is OK for boats, Farm equipment, and other non road equipment but is not legal for use in road vehicles. Exchanging tanks at a convenience store is the most impractical. A twenty lb. cylinder only has 15 lbs. of gas in it and they charge about $18.00 which is about $6.00 per gallon. To get LP at a reasonable price you have to buy it in bulk. As far as the amount of power compared to gasoline this is debatable. Google power from gasoline compared to LP and you will see what I mean. All I know is that with my generator you can't tell any difference on LP or gasoline. On LP the oil never gets dirty, there's no carbon build up, The fuel can be stored indefinitely and with my 500 gallon tank I always have plenty of fuel available for emergencies. Whether it is practical and economical as a boat fuel would depend on a lot of factors that would have to be considered and tested.
     
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