An auxiliary fuel tank has been one of the last truly “necessary” LD farkles missing from my rig. While the ST has a respectable range of 250+ (depending on conditions), the ability to get 350+ miles from a fill-up has become the norm for competitive LD rallies and long certification rides on the clock.

I spoke with a few different custom tank fabricators and came close (but no $2 cigar) to getting one built (due to varying reasons like retirement, etc). I pulled the trigger on a custom tanji-style tank to be built by Boyd’s Welding in Ocala FL. However that tank will not be ready by this July’s Butt Lite IX rally and it had become very clear to me that I would need additional capacity to have a shot at being competitive in such a multi-day event.

Seeing a Sandstorm spun aluminum style tank on a fellow rider’s bike at the Mason Dixon rally helped me visualize a short-term solution and made up my mind for me. When I checked the website, the price was definitely right at $185 for a 3.5 gallon model.

The tank comes with two powder coated spring steel bands for flat surface mounting, a filler neck vent bung, and a 1/4″ outlet bung on the bottom center, for connection to the bike’s main tank.

The purchase was the easy part. The big dilemma for ST1300 owners has been figuring out ways to mount an aux tank. Because the pillion seat locks the rider seat into position, it cannot be replaced very easily like on other bike models. From what I’ve researched, the solutions have been to mount either on the rear rack (which has weight capacity limitations), or using a custom fabricated shelf platform suspended over the pillion seat. Then there are considerations like being able to remove the mounting solution fairly easily on the road in case one needs to access under the seat, and being able to open your rear top-box. Unfortunately, the fabricators that once sold these solutions were no longer in business and I could find no details specifications for any of the mounts.

Having minimal fabrication skills of my own, I called upon my good friend (and skilled machinist) Chris, to look over the situation with me and make recommendations.

“Why don’t you bring it by the shop and we’ll figure something out together?” he says. Wow, don’t ask me twice!

So it was that around midday on a Saturday in June, I met up with him at LW Tank Repair, Inc. in Uxbridge MA, where we grabbed an available bay to look things over. The company makes and services big fuel tanker trucks as its primary business, thought they do smaller odd jobs as well. Chris has long experience as worker of metal. Welding aluminum isn’t in his wheelhouse, but he felt sure we could get plenty done with just bending and cutting some metal stock.

I showed Chris some sample photos from other ST1300 tank installations online, and described what I had envisioned for a shelf over the rear seat on which to mount the keg tank. I hoped to use it for a backrest and needed the top-box to open fully. I was also hoping to adopt the shelf for later use with my custom tank from Boyds.

Once he had the general idea, his creativity took over and it was a pleasure to watch him work in his element, trotting around the shop, turning on this machine or that, grabbing tools from handy (or not-so) locations. There are four frame-mounted bolts that can be used around the rear seat and first step was to build a plate to tie into the rear ones. This is the second plate he cut, as the first was a bit too skinny to be able to adequately the additional bolts to connect the main plate.

The trickiest part (in my mind) was fabricating the forward upright brackets to support the front of the shelf via the frame bolts located under the pillion seat. This required a 90 degree bend, plus a z bend to draw the bracket out of the way of the grab rail latch doors. Chris powered on a huge behemoth of a contraption big as a wall, primary function of which is to press down at enormous pressure to bend metal. (edit: I’m told this is a press-brake)

At first, we tried two 90 degree bends to provide a small horizontal section at the top of the bracket, but this didn’t allow the pillion seat to be removed or installed.

The large main shelf plate was a bit quicker work for Chris, once he calculated the proper inner clearance when bending down the sides to create the flange for bolting to the brackets. Another slight z-bend in the rear half of the plate was needed to draw it down to the brackets while maintaining a more level top surface. He had the great idea of threading the forward holes in the small rear plate and threading stainless bolts up through to create mounting studs. Some stainless wing nuts would make for easy removal in the field.

By late afternoon, this thing was starting to take shape out of nothing but a conversation and a few photos and was looking sweet! Two more wingnuts on the side bolts would make the entire shelf/tank assembly removable by hand when needed, leaving just the rear plate and brackets. For two-up riding, the brackets will need to come off as well, but that’s a simple matter of loosening two bolts under the seat.

Next he measured out the mounting holes for the tank straps and a big 2.5″ hole in the platform for the fuel plumbing. Lacking a large enough holesaw, Chris didn’t blink. He waved a magic wand (so it seemed to me) and quickly set up a Bridgeport machine to gradually enlarge a one inch drilled hole to the desired size.

There’s some extra room between my back and the tank, which I hope to fill with a backrest of some sort. It may be better to move the tank forward an inch, but for now I am extremely pleased with the look and functionality of the solution. Chris did all of this pretty much by eye and with a few scribbled numbers and calculations on scrap pieces for the bend radii. Feeling extremely lucky to have such a great pal, and thanks a ton to the folks at LW Tank for allowing us use of their facility and machines to get this all done in a day!

When it came time to continue the installation at home, I realized there was no stud welded on the tank for grounding against static electricity. I was unsure about the conductivity from the tank to the bike frame, considering the mounting straps are powder-coated. The tank manufacturer confirmed that the coating would likely have insulating properties. I tested for continuity with a multimeter and was able to see full conductivity between the tank filler neck and the bolts going into the bike frame – a great sign.

Nevertheless, I decided on a belt-and-suspenders approach to avoid sadness at tech inspection. I obtained some stainless steel grounding braid and wrapped it round the tank underneath one of the black metal mounting straps, connecting the ends to the vent bung and one platform bolt. This would ensure a wide open path way from the tank surface direction through the bolts and platform into the bike frame.

After some research and asking friends about the fuel connection plumbing, I doodled a design on paper and purchased the necessary supplies. For the quick disconnect, I went with a Jiffy-Tite 3000 series, ordered from Summit Racing, as it seemed light, small and durable.

 

The trickiest part was finding the right-sized connection to go into the lower fuel tank on the ST. Honda was kind enough to put an extra “inspection bolt” on the tank that has been adopted by ST riders as the standard path for transferring aux fuel on this model bike.

Thanks to PlainJay’s build report on the ST-owners forums, I knew the specs of the bolt and some online sources to get a banjo bolt and fitting that would work precisely. I actually bought 2-3 different bolts just in case and ended up using the one with the largest apparent opening for the fuel to pass through.

The inspection bolt on the lower fuel tank used a T50 torx head so a Home Depot run was needed to get the right socket bit – that sucker was on there tight!

After getting all the fuel line cut to proper lengths and connecting all the pieces, I had a nice pigtail with the shutoff valve reachable just behind me on the left side of the bike. When my fuel gauge gets down to around two bars or so, I can reach back to open the valve and allow gravity to pull the fuel into the lower tank of the ST.

The final part involved installing a vent hose to the filler neck. Not shown in the pic is that I looped the grounding strap around the bung before installing the hose and there is a hose clamp in place now.

I’ve found these insulated electrical conduit clamps to have a variety of uses over the years and they made a great way to route the vent hose down the rear fender and behind the wheel for safe overflow. They are loose enough to pull the hose out when removing the tank from the bike.

I used a jerry can to first rinse out the new tank and then put in some fuel to test the flow. It took a minute or so to work through the inline filter, but then I started hearing the musical tinkling of gas flowing into the lower tank. Success!  I’m expecting to get close to 400 miles from a fill-up…we shall see!