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Thread: Smallest, lightest outboard that can connect to external fuel tank?

  1. #1
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    Default Smallest, lightest outboard that can connect to external fuel tank?

    Rather than try to research it myself I thought I'd be lazy and ask here -- Anyone know what the smallest, lightest outboard is that can connect to external fuel tank?

    I'm currently running a Nissan 2.5hp 4-stroke with just the internal fuel tank, and on longer trips that can be a hassle to refuel in wind and swell -- not to mention that it tends to run out of gasoline when approaching a harbor in 25 knots of wind on a lee shore.

    I'm assuming that nobody makes any sort of adapter for these small internal tank outboards to use a small external tank, as I've never heard them mentioned or seen one. But if these do exist I'd sure be interested!
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Can't help you with that Thorne but it would be quick and easy to refuel if you carried one or two of these full of just the right amount of gas and a funnel.


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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    A quick search shows Tohatsu MFS4 has built-in tank, and connector for external tank - weighs 57 pounds (I have no affiliation - just a google search )




    Rick

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Quote Originally Posted by Gib Etheridge View Post
    Can't help you with that Thorne but it would be quick and easy to refuel if you carried one or two of these full of just the right amount of gas and a funnel.
    Au Contraire, mon ami -- in conditions like yesterday on the Delta with 30+ knot winds, a heaving sea caused by an ebb tide going against the wind, in an unballasted open boat, a funnel and pouring doesn't work. Don't ask me how I know this......
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    It may not be what you are after but the Lehr 2.5 propane outboard can run off an external cylinder - in fact I think it can run for about 48 hours straight off a decent sized composite tank.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    No idea if this is a good idea but there's a vid (use google) showing an adaptation that goes through the cap on the motor's gas tank.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    I was doing some research on this a while back. Seems like the cut-off for external tanks is about 60 pounds of outboard. Tohatsu makes a 5hp propane powered OB, they claim 5 hours at WOT for an 11 pound tank, might be worth a look.
    Steve

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    I suspect the small OBs aren’t equipped with fuel pumps. For light-weight, a gravity fed carb is hard to beat.

    I’d go for a transfer tank. Tank in boat with a built in pump. Fuel line to a “thru-hull” on the cap. Could even rig up a return line to prevent overfill. Then, when the integral tank is low, run the in tank pump for a few minutes.
    There's the plan, then there's what actually happens.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Ben - One major problem is that none of these little outboards have a fuel gage, so you can't know "when the integral tank is low"... And the ones that I've seen have enough baffling in the top tank to make eyeballing the level quite difficult.
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    I've never had a boat with a fuel gauge. But I have a watch.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Au Contraire, mon ami -- in conditions like yesterday on the Delta with 30+ knot winds, a heaving sea caused by an ebb tide going against the wind, in an unballasted open boat, a funnel and pouring doesn't work. Don't ask me how I know this......

    This will help

    Screen Shot 2019-06-07 at 6.11.49 PM.png

    Or a siphon.

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    My Honda 2hp 4 stroke consistently runs 75 minutes on a tank at normal cruise. On a narrow river with significant current anchoring is sketchy at best. I start looking for an eddy to hide in at about 1 hour of run time to refill. Second Ian's watch comment.
    If you don't know where you're going, you might not end up there.-Yogi Berra

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Perhaps a transfer pump would make refuelling easier.

    https://www.summitracing.com/parts/m...FUVMDQodQgoEIw

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Quote Originally Posted by Ian McColgin View Post
    No idea if this is a good idea but there's a vid (use google) showing an adaptation that goes through the cap on the motor's gas tank.
    And you can pump it with the primer bulb.
    R
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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Yes, the primer bulb. I once contemplated putting a tee in the fuel line between the fuel filter and the tank and using a standard outboard fuel connection off of the tee that would hook it up to a larger fuel tank from which I could refill the integral tank by pumping the primer bulb from time to time.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    A couple of solutions here, but I like the tee idea better because it doesn't interfere with the tank breather vent. I don't like the idea of drilling a new breather hole because it can allow water in and fuel out. The cap vents are better.

    Having said that, if the breather is a check valve the tee won't work, but I don't think it is.

    https://www.youtube.com/results?sear...r%27s+gas+tank

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    The Johnson/Evirude 4hp twin cylinder 2 strokes are around 35 lb if you can find one used. I spent two hours today headed straight into short bay chop. Refueling would not have been an option.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Thanks, everyone! As Cyclone points out, there are times when stopping just isn't a survivable option. And I just spent over an hour running the outboard in a bucket to get all the gas out of the tank, as I'd just refilled it when we navigated through the tules and arrived at Korth's where we pulled out.

    Sounds like a used 2-stroke might be the answer, but weight is a critical factor as I have to pull the outboard up out of the well before taking the ground.

    The current conditions are much like we had on Thursday --
    ...SMALL CRAFT ADVISORY NOW IN EFFECT UNTIL 4 AM PDT SUNDAY...

    * WINDS...Northwest 20 to 30 kt with gusts up to 40 kt.
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Quote Originally Posted by Gib Etheridge View Post
    Can't help you with that Thorne but it would be quick and easy to refuel if you carried one or two of these full of just the right amount of gas and a funnel.

    If anyone decides to go this route, please don't use a water flask. Use a purpose made fuel container like those used for backpacking stoves. I'd hate to have someone take a swig of gasoline.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?


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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    or a small hand operated pump, (use clear fuel line)
    https://www.dubro.com/products/kwik-fill-fuel-pump

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Thanks again, all. Looks like the best option is the external tank hookup through the fill cap, so I'll investigate. No solution to the "full internal tank at the end of a trip" issue other than to pump it out, but if I ran the internal tank fairly empty near the end of an outing I could top it off with the squeeze bulb to the external tank and keep the internal tank fairly empty. Hmmmm.....
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    You could fit a pulse type fuel pump and use a regular remote tank also.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    If you check out the microcruising web site, 'Little Cruiser' has an external tank which is manually pumped into the ob's running tank. If you do something similar it would allow you to continue with your existing ob but effectively to have an unlimited range.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    My experience:
    I had an Honda BF 2,3 hp aircooled outboard. Weight 13 kg, 1 liter fuel internal tank. Nice light motor. 1 liter gasoline for about one hour full throttle. Used it on three small wooden boats I built and used it with motor in the lagoons of Venice (Italy). Boats: Auray Punt (Phil Bolger), Amberjack/Sickleback Dory (Iain Oughtred) built with motor-well, Spike/Pike (Iain Oughtred). Motor performed well on those boats, but for me following three disadvantages:

    - Fuel tank internally: Very difficult to fill if one is out there with waves/swell/current and wind. Spilling gasonine... not good.
    - Power: If you are motoring against wind/waves and current motor was at its limits with Amberjack-Dory. It took me some while to get back to harbour.
    - Motor air cooled: Quite noisy

    Looked for a system to overcome refueling-problem. Solutions above considered but finally not an option for me as power of motor for my 12 feet to 15 feet boats was an issue.
    Finally came to the conclusion to change Honda 2,3 hp to an 5 hp Mercury with external fuel tank.
    Advantage: Safety, refueling, power, noice
    Disadvantage: Weight (Mercury 5 hp without fulel tank: about 30 kg).
    Last edited by Pateplumaboat; 06-10-2019 at 05:50 AM.
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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    I don't like to be repetitive but the Lehr 2.5 weighs 38lb (17kg) and will run directly, without any fuel cap bodging or transfer pumps, from a range of external tanks giving run times of between 1 hour and 20 hours at WOT.

    https://golehr.com/lehr-2-5-hp-4-str...tboard-engine/

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Quote Originally Posted by Clarkey View Post
    I don't like to be repetitive but the Lehr 2.5 weighs 38lb (17kg) and will run directly, without any fuel cap bodging or transfer pumps, from a range of external tanks giving run times of between 1 hour and 20 hours at WOT.

    https://golehr.com/lehr-2-5-hp-4-str...tboard-engine/
    The 5 hp Lehr would have been an option for me. Available in Europe and for what price?
    Hay mas tiempo que vida!

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Quote Originally Posted by Pateplumaboat View Post
    The 5 hp Lehr would have been an option for me. Available in Europe and for what price?
    Certainly available in the UK at £630 for the 2.5 and £1150 for the 5. I think I have seen them in Italy too but not sure about Austria.

    https://nestawayboats.com/shop/lehr-propane-outboards/

    Once you get to 4/5hp there are quite a few motors which can run off an external tank - it is the 2.5hp Lehr that is a pretty unique proposition.
    Last edited by Clarkey; 06-10-2019 at 07:17 AM.

  29. #29
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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Quote Originally Posted by Thorne View Post
    Rather than try to research it myself I thought I'd be lazy and ask here -- Anyone know what the smallest, lightest outboard is that can connect to external fuel tank?

    I'm currently running a Nissan 2.5hp 4-stroke with just the internal fuel tank, and on longer trips that can be a hassle to refuel in wind and swell -- not to mention that it tends to run out of gasoline when approaching a harbor in 25 knots of wind on a lee shore.

    I'm assuming that nobody makes any sort of adapter for these small internal tank outboards to use a small external tank, as I've never heard them mentioned or seen one. But if these do exist I'd sure be interested!
    Hi Thorne,

    My knowledge is getting outdated, but a few years ago my Honda 5 hp was stolen and I looked around at other motors. As I recall, the Yamaha 4 hp was very attractive, lighter and quieter as well as having both an internal tank and external hook-up. I ended up with another Honda because of the terms of my insurance cover (if I bought the same model as that stolen, they paid all but the deductible for a new motor, if I bought anything else they only paid the value of a 20 year old motor...) so my knowledge is limited.

    I did once use a 4 hp Yamaha once, when moving John Guzwell's Trekka for the Maritime Museum here in Victoria before a boatshow. I started the motor then went below to get things ready to go, when I came up into the cockpit I couldn't hear the motor running until I looked over the transom to make sure!

    Cheers,

    Jamie

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Quote Originally Posted by Pateplumaboat View Post
    The 5 hp Lehr would have been an option for me. Available in Europe and for what price?
    I've heard of severe quality issues with the Lehr outboards but this may have changed. I'd look carefully at recent owner reviews before I bought a Lehr outboard. I notice that West Marine no longer carries the Lehr brand of outboards, that is where I read many of the bad reviews.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Quote Originally Posted by Mike V. View Post
    I've heard of severe quality issues with the Lehr outboards but this may have changed. I'd look carefully at recent owner reviews before I bought a Lehr outboard. I notice that West Marine no longer carries the Lehr brand of outboards, that is where I read many of the bad reviews.
    I noticed that but then again almost all small outboards seem to have something wrong with them according to many reviews. They certainly don't seem to have the pedigree of the more established outboard brands. If I wanted a 5hp propane outboard I would probably go for the Tohatsu.

    In fact, the ideal for me would be the Tohatsu 3.5 running from a propane cylinder. Maybe they will do it?
    Last edited by Clarkey; 06-10-2019 at 03:17 PM.

  32. #32
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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Looks like they make some "extended run" gas caps for generators, might also work on outboards but it is probably easier to fab it up yourself - https://smile.amazon.com/dp/B06VTS92...1-b9b22186d32d





    Yes, IF I was buying new I'd do some serious research on the propane outboards, but suspect they suffer from the "Version 1.0-itis" so sadly common to new technology.

    YouTube - Shawn Braden2 years ago (edited)

    so far two carborators replaced, oil pressure switch replaced, the internal starter no longer works , the forth repair shop is a drive 2hr where the engine is sitting awaiting more trouble shooting. also, the initial fluid change was very difficult, the original oil filter was over tightened, same for the lower unit drain. also, they are now telling me I am required to use liquid draw tanks, before I bought the engine they assured me I could use vapor draw (blue rhino) . this company and their products are best described as low integrity.

    Amazon -
    1.0 out of 5 starsAlso really disappointed
    [COLOR=#555555 !important]May 4, 2015[/COLOR]
    We also purchased the 5 HP Lehr for our dinghy for use in the Pacific Northwest, from West Marine. We used it for about 2 hours (one longish round trip around an anchorage) and it seemed not to have much power. We used 2 fuel canisters, pretty much as predicted, and changing them on the go was fine. However, on the way back, it died and would not restart. We had to row ourselves back to port, and asked Lehr to refer us to a warranty repair place. This was the beginning out our Lehr nightmare.

    They don't have many repair places, and the one they gave us was not close by, but we went anyway. That place took the engine for the rest of the summer, and finally said Lehr helped them diagnose the engine had a leak in the fuel system (!!) and they tried to fix it. We meanwhile asked West Marine to take it back or exchange it, and like the other customers we were denied.

    We tried the motor again on our next outing and sure enough the problem of not starting or idling well, sputtering and dying and leaving us stranded was still there.

    We took the engine to Seattle and this time the new repair place essentially replaced all the fueling components under warranty. We tried the engine again, and it ran better, but still doesn't start well, and worst of all, it will allow a lot of propane to burst out of the fueling tube when disconnecting the tank (as if the check valve is not functioning properly and is trapping lots of pressurized propane in the line before the carburetor). This is extremely dangerous as a huge cloud of propane spews out, and could go into your bilge, etc. When that happened I really lost trust in the engine altogether, and am leery of using it with my family nearby. Our mechanic says Lehr won't answer his calls.

    We hope to get it fixed, but since then our marine industry sources say they are stepping away from this product until they address the quality issues people are experiencing.
    Last edited by Thorne; 06-11-2019 at 02:13 PM.
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  33. #33
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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    How about a vented gasket that marries to top of outboard when fueling with MSR canister - 11 oz of fuel into the tank would be less than 10 seconds, done with one hand and little to no spills.

    DA9C816C-7AC9-4B75-955B-B95FD6307204.jpg

    I plan to do this with my 3.5hp long shaft mercury. I’ll make a video.
    Last edited by Ted Hoppe; 06-11-2019 at 01:53 PM.
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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    I did the mod to the fuel cap today and it works quite well. I used a big bolt as a thread cutter in the nylon cap, and the fitting seems to be pretty secure once I wrestled it into the hole.

    Before -


    After (I added a small vent hole in the cap after this pic was taken) -




    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

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    Default Re: Smallest, lightest outboard that can connect to external fuel tank?

    Bingo!
    I suspect you could place your aux tank at a higher level and just start a siphon with the hand pump and voila tank is filled.
    Is there a way to vent the existing tank, or will you just switch caps?

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