Quick-connect external fuel tank for generator

Quick Connect Generator External Fuel Tank For Extended Run Time

The concept of a generator external fuel tank – adapting remote fuel tanks to generators – struck home with me while dealing with a portable Coleman generator, which had a 5 gallon built in tank.

Guest article by ‘Bogan’

To keep it fresh, I had to drain the durn tank from time to time and use the drainage in beater lawn mowers.

Until one day the light bulb turned on!
What if I could use my boat gas tank(s) as the fuel source for my generator?

– For the last 50 some years I have been a boater, with outboard motors that had a remote tank.

That way I need not fill the built-in tank with gas that would, no doubt, grow stale.

Then Hurricanes Francis and Jeanne hit in Florida in the early to mid-2000’s. We were without reliable power from Florida Power and Light (the utility), and had to generate power 7/24.

One problem was limited fuel reservoir in the generator. Another problem was you had to let the generator cool down before refueling, and even then there was spilled gas and the potential for explosion. Lots of danger.

Sooooooo. What if we were to rig up the generator the same way we rig a boat motor: when we want to run it, just connect the remote tank and go! And when it came to refuel, just plug a new tank in? Taa daa! Enter boat fuel tanks!

Fuel Quick Connect for Generator External Fuel Tank

The first thing was to set up a quick connect in the generator. My fuel tanks are for the OMC outboards (Johnson/Evinrude, yeah I’m “older”!)

They are called “OMC quick connect”.
(view on amzn)
Brass Quick-Connect Tank Fitting 1/4-Inch NPT Male Thread for Johnson/Evinrude/OMC
With this rigged up I can simply clip in a new tank whenever needed!

If you would like to go this route, here’s an external tank, hose, and connectors:
(view on amzn)

Attwood Portable Marine Boat Fuel Tank, EPA-Certified – 6-Gallon

Attwood Universal Fuel Line Assembly Kit with Tank Fitting

Johnson/Evinrude/OMC Fuel Hose Fitting by Attwood

If you want to go with even a bigger tank, that will give you more running hours:
12 gallon low profile fuel tank by Scepter Marine
Attwood 12 Gallon Low Profile Fuel Tank

You can also save some money by buying used outboard motor tanks at yard-sales, Craigslist, etc.

External Fuel Connection to the Generator

One key issue will be the connection between the hose coming off the external tank, and the hose leading from the built in tank of the generator to the carburetor. To solve this riddle, here are a few options:

Option 1 – Purpose built external fuel tank for your generator

Simply buy something purpose built for your brand of generator that flows the gas from an external tank. This one connects to a generator (e.g. the Honda) through a special fuel tank cap and into the internal tank of the generator.

External fuel tank for Honda generator
An example of a fully made up kit for a Honda generator (and a number of other models) is:

Extended Run Generator System

The key component for a system like this is the cap leading to the internal tank, this one with a hose barb:
Honda generator fuel gas cap for external tank
Extended Run Fuel Gas Cap

This particular one does not have a quick disconnect feature but given the cap screws on and off quickly, it may not be necessary.

Option 2 – Direct to Carburetor connection

Fully drain and disconnect internal tank, and connect remote tank directly to intake hose to the carburetor.

There are two basic kinds of fittings: “hose barb” and “quick connect”. The hose barb is more permanent. The quick connect is…as its name suggests.

Hose Barb

For a simple “hose barb” connector, consider something that looks like this:
Barbed straight connector pipe fittings
Barbed Straight Connector Brass Fittings

It will need to be kept in place by a hose clamp, or stout zip tie.

One issue may be differing hose sizes between what’s on your generator and what’s on your boat tank.

It will be common that the hose leading to the generator’s carburetor has 1/4″ I.D. inside diameter. The hose leading from the boat tank has a 3/8” or 5/16” I.D.

In this case get a variant that “steps down” the hose size or is a “reducer fitting”. This is hard to find, but Amazon is your friend and the big box hardware stores also have walls lined with options.

BTW, always get brass, not plastic, for the toll the chemicals in the gasoline take on plastic.

In all cases the hose should fit quite tightly on side of the barb or dangerous leaks (enhanced by the vibrating motor) may result, creating a hazard.

Quick Connect

For “quick connect” style you’ll need to mate your quick connect female fitting on the tank to a compatible male fitting on the motor.

I’m an OMC (Johnson and Evinrude) guy, so the connector at the end of the hose coming off my tank looks like this:
OMC and Bombardier female hose connector
5/16 inches Barb Female Fuel Line Quick Connector

It will connect to a fitting that looks like this:
Quick-Connect Tank Fitting
Brass Quick-Connect Tank Fitting 1/4-Inch NPT Male Thread for Johnson/Evinrude/OMC

However, note that it has a threaded fitting. To this one would attach something that looks like this female adapter barbed fitting:
1/4 inch NPT barbed fitting female adapter
Brass Hose Barb Fitting, Female Adapter

– making sure the barb size matches your carburetor intake hose.

Note that when the connectors are disconnected from each other, they are designed to self-close, limiting spills.

Other outboard manufactures (Mercury, Yamaha, Honda, Tohatsu, etc.) have different connector styles and sizes. The principle is the same though: just depress some sort of a lever and pull the fitting apart!

Option 3 – Tap Into Fuel Line Of Internal Tank

This option involves tapping into the line between your internal tank and the carburetor, and making it possible to continue to use the internal tank but also attach a quick connect-equipped boat tank.

For this you need a hose splicer such as this:
Brass 3-way Tee, 1/4 inch
3 Way Union Fitting

3 way metric hose barbed fitting
3 Way Hose Barb

BTW if your in-line hose is ¼ inch, then the 6mm fitting is your huckleberry.

To the flange that points to your boat tank connection, add a short length of hose and then the “quick connect” set up outlined above. I like to make the connecting hose long enough to zip tie it to the frame of my generator.

A note about the hose leading out of the gas tank: you can buy hose of pretty much any length you want. Plenty of good reasons for this: safety, to gain elevation for the tank, convenience of storage, etc.

BUT if the hose has a 5/16” or 3/8” inside diameter and gets much over 15 feet long, you may want to step DOWN the hose size to ¼”. I learned this the hard way when rigging a boat with a gas tank way in the front and used a long hose. The motor would starve for fuel because the fuel pump was working overtime pulling fuel all that distance. The situation cleared up when I downsized the hose to a smaller volume.

Another note on quick connectors. I have heard (but not tried out) that air compressor fittings can be used for the quick disconnects. This sounds dangerous to me, as it would not be an intended use for the design, but my fears could be misplaced. I would appreciate anyone with firsthand experience on this to share their knowledge.



[ Read: Fuel Treatment for Generators ]

[ Read: Sea Foam: All Purpose Fuel & Motor Treatment ]


  1. Very clever. Keep in mind that some generators use gravity flow from the tank to the carb, and for these, it will be necessary to locate the external tank ABOVE the level of the carburetor, and use the inline primer bulb to establish fuel flow to the genny. Once established, it should keep going by siphon. Other generators have fuel pumps and you could just set the tank on the ground.

  2. Wow Bogan, good idea. This set-up that would be great for us. It takes two people to lift and pour the gas when it needs filling. I like this concept better. Thank you.

  3. Bogan;
    Some good ideas, as someone mentioned, Peanut Gallery, fuel is heavy and allll so much fun to pour into a Gen-Set at 3:00am in the dark.

    A comment about using Air Fittings with fuel ‘DON’T do it !!!!’; the rubber gaskets are NOT made to be compatible with fuel. Things go Boom all the time because someone takes a shortcut.

    Lastly, why ohhhh why did you have to mention a Boat Fuel Tank, I have a particular aversion to ANYTHING to do with Boats….. 5 total Boating accidents involving the loss of firearms and ammo, so NOT happy with Boats. I need to find a Brass, Stainless, and Lead magnet to recover that stuff at 400 feet down.

  4. So I looked but didn’t find a cap for a Briggs and Stratton generator. Anyone know of one?
    Also it’s gonna have to seal better than the one on it or this isn’t gonna work cause the tank will overflow.
    Or is it better to tap into the fuel line?
    This interesting and I’m trying to figure it out now.

    1. Matt;
      Tap the fuel line, that way there will be no fuel in the tank to go bad later.

      1. Ok
        My fuel don’t go bad. I use PRI-G. I’ve tested it to 5yrs. It says 6 but I couldn’t stand it anymore so I used it lol.
        If I tap the line and use both external and internal then it should really run a while huh?

        1. Tomas –

          Pri-G is sold mostly online, it is a fuel treatment not a fuel. Do NOT use AVGAS in a generator. Regular low-octane gasoline is best.

  5. We have used this method for several years now. It works great at the duck club where our older uncle cannot lift the fuel cans. It makes it so much easier to refill the boat fuel tank rather than have to hold the gas can to the generator (and even with the anti-spill nozzles, they still spill a lot!).

  6. I like this idea of an external fuel tank. I’ve heard that the plastic fuel tanks on generators sometimes crack with age. A quick-connect in the fuel line would by-pass that problem, should it occur. Probably would need a check-valve (back flow preventer) between the internal tank and quick-connect to prevent gas from flowing from the external tank to the internal tank.

      1. You are right. I didn’t think of that. If you have an in-line fuel shut off, just put your Tee for the QD below the fuel line shut off valve.

    1. Tommyboy,

      Could you elaborate please. Are you speaking of the electrical generation portion of the unit or the engine? Under heavy load, or in general usage?

      I’ve run mine 12 hrs plus a day for almost 2 weeks at a time, only changing the oil once during this period, with no ill effects. Internal combustion engines, as long as lubrication and normal operating temperatures are maintained, shouldn’t be affected by the length of time being run in one stretch. The electrical generation portion, I really don’t know how it stands up to long term running. To what extent should I be concerned? Do you recommend periods of rest? How long and how often?

    2. Tommyboy, good point. Influenced by the maintenance schedule, fuel type and supply, size of the unit, and it’s intended usage. Consulting the owner’s manual for the manufacturer’s recommendations.( yeah me too, if you can’t figure it out, get the owner’s manual 🙄)
      Possibly an idea for the Project Farm guy on YouTube.

      1. I just ran my princess auto generator ran my in minus 30 Celcius for 31 hrs waiting on power to come back on… ran furnace, fridge, heat trace tape, well pump and septic pumps… only used 40 litres of gas!I was amazed! Obviously once power was on I disconnect the wiring to house and did oil.change. lol

        1. Oh Wow! Princess Auto in Canada is one of my customers; in turn they treat their customers very well indeed. What a great and amazing testimonial. If you feel like spreading the word, online reviews are great. OTOH, if you ever have a question or issue with that gennie, perhaps something others in the forum could benefit from (and if it’s ok with Ken, of course), post it in the weekend free-for-all and maybe others will benefit from the exchange.

    3. Exactly correct Tommy! Why aren’t more people as observant as you? There is a big difference between ‘portable’ class (intermittent use), and “standby class” (continuous, but $$$$)

      1. Tmc
        Ive just done my research.
        I like heavy duty equipment, dont get disappointed that way.
        Tommyboy AKA Kulafarmer

  7. Timing on this is great as we are looking for a small generator to mount on the rear bumper of our travel trailer. I’m already in the process of building a rack for the fuel tank for out Nissan Outboard. The plan is to carry our inflatable dinghy in the back of our Dakota along with the outboard but don’t want to carry fuel in the passenger compartment. This setup should do nicely.

  8. Just a thought, for those for whom weight is an issue. Although most outboard tanks are 6 gallons and up, you can also get them in smaller sizes like 3 or 4 gallons. Much easier to lift and haul around. The fittings are all the same. I ask Ken if he would be good enough to post a link.

  9. Yes, But, only if it’s within 24 hours AND only if you haven’t clicked on someone else’s Amazon link between that time. Hope that helps…

    That said, if you actually add it to your cart (while not actually checking out for awhile), I supposedly get credit even up to 90 days later (I think)…

    1. Ok man. I’ll try and remember to go back cut n paste into it then.

  10. good deal…fla boy….im fla boy to…fish.crab mullet…you name I did it…net too…I had a Honda generator tank rust out…dam I use my skiff fuel tank for that dam generator….in of that cheap steel rust bucket.fuel tank…tank only two years old…china……later my friends…….usmc…nam….

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