Yamaha outboard conversion to LPG

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

  1. sailor305
    Joined: May 2012
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    Location: Miami Beach FL

    sailor305 future cat builder

    Recently I have seen an outbord motor running with LPG.
    A 9 lbs tank provides about 50 hours running time.

    Is it possible to convert 9.9HP Yamaha high trust to LPG?
     
  2. CatBuilder

    CatBuilder Previous Member

    Yes. Replace the carb with a propane regulator. Try a Google search to see if someone might be selling ready made kits for this.

    I am a big fan of propane as a fuel and would love to run my boat and systems on it. Tell me, what is your strategy for refilling tanks? When I looked into this, I could not find propane at fuel docks.
     
  3. sailor305
    Joined: May 2012
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    Location: Miami Beach FL

    sailor305 future cat builder

    refueling

    Hello Cat builder,

    thank for your reply.

    Indeed refueling isn't that easy and you have to go to gas stations.
    However, with the rising fuel prices it may getting better in the near future.

    Abroad is it much easier because some body will take you to the refilling place but you should have adpters.
     
  4. CatBuilder

    CatBuilder Previous Member

    Thanks for the response 305. I thought maybe you had found a creative way to fill propane as you travel. It's an ideal fuel and your engine will run trouble free for years on it.

    I wanted to install a home size tank on my boat to run engines and systems, but I would have needed to fill it at fuel docks, so I was unable and am stuck with gasoline.

    Good topic. I wish it was available at all fuel docks VIA refill hose.
     
  5. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    Most propane companies in every town have trucks to deliver it to the customers own tanks.
    No reason they could not drive down to the docks to fill up your tank(s). Usually have a 100' to 150' hose.
     
  6. Frosty

    Frosty Previous Member

    All Bangkok taxis are propane-- LPG-- and there is gas --gas stations everywhere.

    Catch up America.
     
  7. CatBuilder

    CatBuilder Previous Member

    Rasor, have you ever cruised before? Just finding fuel docks that are convenient is hard enough, never mind calling ahead and trying to convince a local propane company and marina (who you are not buying fuel from) to let you do this.

    Both the propane company and the marina would object - and if they do, you lose all your food as well as your propulsion.

    Very difficult to do.

    Frosty, we have plenty of propane stations. Why do you think I am a fan? It's because i use it all the time on land.

    How many marinas in your area have a propane filling hose dockside? I don't think you are more advanced in marine services than the States. We are just about the most advanced im thr world when it comes to marine services.
     
  8. Frosty

    Frosty Previous Member

    There is no LPG station at waters edge. All fishing ports will supply diesel, sea boats use diesel. Petrol is very inflammable + explosion+ boom = hospital

    I would have thought that small point to have been considered in your chosen cruising grounds and choice of engine.

    One of the reason people are reluctant to use electric cars. where do you re charge.

    Can you get insurance on tanking such an amount of petrol.
     
  9. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Yes, it is possible, but the investment is quite a burden for the amount of fuel savings because this is only a small engine.
    You need the smallest pressure regulator you can find, I think it comes from Italy. Because you need some means to get home when your gas bottle is empty, keep the carb and gasoline plumbing. Install a gasoline valve close to the carb and install an LPG injector tube in the carb housing just before the throttle valve.
    The regulator is mounted on top of the gas bottle and is adjusted for zero pressure, i.e. no gas flows unless the air pressure withing the carb is lower than the ambient. The regulator has a push button to provide a small gas flow needed to start the engine.

    The gas bottle needs a lot of air to prevent frost, especially in cold climates; it must stand upright, so no liquid gas can enter the regulator. Larger regulators for passenger cars are connected to the engine cooling circuit, they accept liquid gas as well.
     
  10. Petros
    Joined: Oct 2007
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    Petros Senior Member

    I bought a kit recently to covert our generator to propane (when the power goes out we have a 500 gal propane tank on the prop already, but mostly the crap gas they sell now ruins the carb in small engines).

    The kit was pretty costly, almost as much as the generator itself. It consist of a few simple fittings and hoses that I think could be bought separately or made in a home shop. There is just a tube that replaces the carb main jet, with an fine adjustable valve on it. That valve has a fuel hose that goes to the regulator. The regulator looks like two small pie pans screwed together, in it is a diaphragm with a needle valve. The regulator adjusts the fuel flow based on manifold pressure. The whole thing is simple, and most of the parts you can likely salvage off an old propane barbeque or similar device.

    You drill out the old carb housing, right through where the old jet goes into the venturi, and epoxy in the tube with the adjustable valve into the carb housing. It is like a fuel injector, rather than having a float bowl, needle valve, fuel jets, the gasious fuel is injected directly into the throat of the carb. The only "trick" is to adjust it to the demands of the engine. If you want to keep the ablity to convert back to gasoline I would find a junk carb to convert to propane use, and than swap the carb when I want to change fuel. You ruin the carb when you convert it for propane use.

    If I do another one I think I will save $300 and find or fab the parts my self. A car conversion kit is similarly simple, and costly: $800 for small carb engine, and about $2000 for a fuel injection conversion kit. None of these cost include the tank.

    It seems to me, with a small boat, you can use the portable propane tanks used on campers or barbeques, and just bring a full one to your boat every time you go to use it, swapping out the existing one.

    BTW, this will not work with a two stroke motor. There is no way I know of to lubricate the internal parts when using gaseous fuels, so it is only reasonable to do with 4 stroke small engines.
     
  11. Frosty

    Frosty Previous Member

    Your not supposed to drill out the carb-- you drill out a hole in the manifold as close to the carb. the carb should still work as before when you don't have any LPG.

    Did you actually do this or some one down the pub did.

    The main jet in the carb is so placed to be in the venturi and when the throttle is opened the fuel is sucked into the engine from depression . The LPG needs no such thing.
     
  12. Petros
    Joined: Oct 2007
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    Petros Senior Member

    I well know how the carb works, these were the instructions that came with the kit. The carb was junk anyway, ruined by the crappy gas they sell us here (inside all corroded and not rebuildable). You take out all of the check valves, floats and other jets and fill them silicone sealant. A new carb is not too costly, and I figured if I ever wanted to go back to gas I would need a new carb anyway.

    If you put the injector directly into the manifold down stream of the carb, how are you going to throttle the engine Frosty? This is not a diesel, it was a gasoline Techumca engine. Now propane, to be fed either from a portable tank, or from the 500 gal house supply tank.

    It only cost about $1.80 a gal to have the propane delivered, I might buy another 500 gal tank, and convert our cars to run off of it too. The more I buy at once the less it costs per gallon. I just need to rig a way to fill smaller tanks from the large one.
     
  13. Frosty

    Frosty Previous Member

    YOU said that it was fueled by the regulator feeding from manifold vacuum!!!

    With the butterfly valve you still got that. Diesels dont have inlet manifold butterflies , you can take the manifold of,--f infact take both of them off exhaust and inlet and it will still run fine.
     
  14. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    How is the amount of propane metered to achieve the needed ratio of propane to air if the propane is introduced into the manifold? With the propane introduced into the manifold won't the amount of propane increase when the throttle is closed and intake manifold pressure drops, and decrease when the throttle is openned, which is opposite of what is needed?
     

  15. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Frosty, your info in post #11 is not correct.

    Simple LPG systems feed the gas before the throttle valve because the air pressure there is below ambient when the engine runs. The tube may be installed as Petros has described, but then you cannot use gasoline anymore. It is better to drill a hole further away from the venturi in such a manner that the LPG tube enters at approx 45 degrees and ends just in front of the gasoline jet.

    The vacuum there is still sufficient for the diaphragm in the regulator to open the LPG valve. Adjustment for the correct mixture is done with a regulator screw on the exit port of the regulator or at any point between the regulator and the injection tube; it depends on the construction of the regulator.
    Although the regulator looks like any ordinary propane type, it works slightly differently. The ordinary regulator supplies a fixed pressure of 35 or 50 mb, the one for LPG only opens if the exit port is below ambient pressure.
     
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