Auxiliary fuel tank


  • I recently used the aux tank on a 3,000 mile (5,000 km) ride. It performed flawlessly. I used the 1/4″ fuel line, and I did notice that if I let the mains draw down to empty prior to turning on the aux tank, it would take a long time for the aux to drain. Consequently I learned to turn on the aux tank after approximately 100 miles (160 km.). No problem then with having all the fuel available all the time.
  • Of course, this problem would be eliminated by using 5/16″ lines and fittings, as flow rate would increase with the larger diameter lines and fittings.
  • I’ll eliminate the larger round filter for dirt, since this didn’t seem to be a problem on initial use with the tank.
  • The tank will hold 2 U.S. gallons (7.57 liters) when on an angle sitting on the kick stand on my Harley-Davidson.
  • I grounded the brass tank fitting to the frame using copper wire.

The tank in this article is one of the older, original tanks from Tour Tank in Tucson. If you check out Bill’s site link on the sidebar, you’ll see plenty of newer tanks.

If your bike is fuel injected, you can’t use this method to run your fuel hose. You’ll have to remove your fuel tank and tap it with the appropriate fittings for your hose run from the auxiliary tank.

I wanted a 90 degree elbow on the tank outlet, so I bought a 1/4″ FIP to MIP Street Elbow at Home Depot. This screws into the bottom of the aux tank, and accepts the brass outlet that is supplied with the tank. I used JB Weld on the threads of the 1/4″ outlet for a secure and leak-proof fit. This is a PERMANENT cement.Elbow

Be careful not to tighten the brass elbow fitting into the bottom of the tank too securely, as this could cause problems with the nylon receptacle portion of the tank outlet.

Thread sealant I used a Teflon pipe thread compound on the fitting that screws into the tank bottom. Check the directions to be sure the thread compound is good for fuel.

When putting the paste on the threads, be sure not to get paste past the end of the fitting, as this could block the fuel flow.

DO NOT use Teflon tape on any fittings. The gasoline will destroy the tape and the fitting will leak.

I don’t like the nylon “T” that comes with the kit, consequently I’m trying to find a brass “Y” that will cut down on the fuel hose angle where it is spliced into the fuel line under the FLHT’s five gallon tank. There’s not a lot of room under the tank for extra fuel lines, and I don’t want the installation to look too unprofessional.

I added separate in-line dirt and fuel filters. The filter on the right will go into the line first and is for big chunks. It’s not directional. The filter on the left is directional, indicated by the flow arrow.

I bought a self-closing quick-disconnect fuel coupling for the fuel hose. It comes with the 1/4″ adapters.

I replaced the supplied shutoff valve with the Motion Pro 1/4″ fuel shutoff valve. Here’s the fuel line run with (from top right to bottom left) the fuel filters, shutoff, and quick-disconnect.

I ran the fuel line along the left passenger grab rail of the FLHT using tie-wraps. The fuel shutoff is an easy reach behind me when riding. I attached it with zip ties and the handle pointing down when off so that it wouldn’t inadvertently get turned on by an errant bungee cord. To remove the tank I’ll cut the three tie-wraps and undo the quick-disconnect.

I picked up two 15″ (38 cm) FAT STRAP flat bungees to hold the aux tank on the trunk rack.

Here it is, strapped down with the bungee cords. It holds exactly 2 U.S. gallons when leaning on the kickstand.

9 thoughts on “Auxiliary fuel tank

  1. I have a Harley Electraglide standard with fuel injection. After seeing comment on not workin on FI I looked at my tank and there is an equalizer line from one tank lobe to the other. Can’t I tie fuel line from aux tank into there?

  2. Tom, I don’t really know. Any aux tanks I’ve seen added to FI have been through an adapter on the tank. Whether such a setup as you propose would work, I have no idea.

    Just so you know: The setup I’m running is on a ’95 bagger, which is NOT fuel injected. The gravity feed works perfectly in that situation.

    You might want to ask over at this forum:

  3. I, too, have a 2008 Electraglide which has EFI; is it possible to attach fuel from an auxiliary gas tank at a fuel line under the main fuel tank? Thx for your help my hack go further before fueling! Hack

  4. No, you can’t do it that way. You’ll need to add an actual adapter to your fuel tank to make use of an aux tank on a fuel injected engine. You can’t gravity feed fuel into an existing fuel line on an FI bike.

  5. Twolane, why can’t I, using gravity feed from an 12-gallon auxiliary fuel tank mounted in my Tour Pak, attach that to a petcock installed&welded into my main gas tank? Any chance? Thx – Hackkman

  6. I know nothing about fuel injected systems on the Harley. My aux tank mod is for an unpressurized/gravity-fed carbureted fuel system only.

    I’m sure if you do a google search for adding an aux tank to a fuel injected motorcycle, something should come up that will help you out.

    Sorry I can’t help more than that.

  7. I actually just uninstalled my 4 gallon tour tank off my 05 suzuki s50 Boulevard. The fuel line had started leaking and it was just easier replacing the original and pulling the tank off since I don’t anticipate as long rides at the moment. I’ll keep the mounting hardware but I’m liking slim line hosing rather than the steel braid I had just for ease of use.

    As for the fuel injection issue, it has to do with the tank pressurization, and since there isn’t a petcock, there is no easy place you can splice in without issues. [ edited ] if you are FI you can get some issues with fuel flow and possibly backflow into the aux tank [edited ] .

  8. Thanks, Jason. I didn’t want to get into the specifics because of liability, thus the editing of your post, due to my reluctance.

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