How I added an auxiliary fuel tank
to my ’89 GL1500 Gold Wing

by Terry Simpkins

In preparing for an upcoming trip to the Arctic Circle, I realized that one of the ‘legs’ of the trip was longer than my bike could make between fuel stops. The segment between Dawson City, Yukon and the settlement of Eagle Plains, Yukon is 231 miles. On a good day, 200 miles is about all I can stretch from a tank with any safety margin. Given that the Yukon near the Arctic Circle is NOT where you want to be flirting with running out of gas, meant I was going to have to extend my fuel range. That means an auxiliary fuel tank.

A friend had decided that his days of extended mileage were over, and he wanted to sell his auxiliary fuel tank. Perfect timing. I bought the tank, and then had to get it installed. This is a description of my installation process.

The major things you have to determine are:
- Where to put the auxiliary tank
- How to mount/secure the auxiliary tank to the bike
- How to get the fuel from the auxiliary tank to the bike

I decided to mount the auxiliary tank on the rear seat, since that was the way the auxiliary tank was designed and built to be secured with straps to the passenger hand holds. Again this seemed to be the way the tank was designed.

I decided to use a gravity feed from the auxiliary tank to the stock tank. This would have two big advantages:

1) Simplicity – no pumps to get fuel from the auxiliary tank to the stock tank
2) I could use the stock tank fuel gauge to keep track of fuel status

With whose decisions, I set off on the installation. The following are the major steps with photos to highlight the process:

1. Remove the seat
2. Remove the stock tank top
   • a. Disconnect the battery first to eliminate the possibility of sparks
   • b. Disconnect the out fuel line and plug the hose
   • c. Disconnect the fuel pump power and fuel reserve light
   • d. Pull the assembly up out to the fuel tank and place into a bucket of some sort so fuel doesn’t get all over everywhere

In order to get the fuel from the auxiliary tank into the stock tank, I needed to mount an inlet fitting somewhere on the top of the stock tank. The fuel pump mounting plate seems the logical location, because I can work on it off the bike, and if I screw-up, it is easier to replace it than the fuel tank.

Available space on that plate is very scarce due to the large bracket on the bottom attaching the fuel pump to the place (photo 1)

In order to make room to mount the fitting, I had to grind out a ‘hole’ in the bracket. I then selected a fitting, and drilled the hole in the top of the fuel pump plate. I had to construct a nut with a ‘necked in’ shoulder that would secure the fitting to the plate without getting in the way of the sender connection. You may find a better way to do this, but I was going to be absolutely certain this fitting could never vibrate loose and leak. I also used a fuel resistant epoxy to seal between the fitting and the plate.

I used ¼" fuel line tubing from the new fitting to the auxiliary tank connection. The auxiliary fuel tank already had ½ of a quick disconnect/dry brake connector. The guy I bought the tank from had left the other end of the connection on his old bike when he sold it, and couldn’t remember where he got the connector.

It turned out to be a marine fitting available at Boaters World and West Marine. Check there, they have a good selection of connectors to choose from. The down side is that the ones with barb hose fittings all use 3/8" tubing. So you should either plan on some sort of reducing connector for the two hose sizes, or plan on using 3/8" tubing throughout. Knowing what I know now, I would have used 3/8" tubing throughout.

Along with the auxiliary tank, I got a seat for the GL1500 that had been slightly modified. The padding on the rear section of the seat had been shaved down to let the tank sit slightly lower, and the piece that filled the void between the seat the passenger backrest on the trunk had been removed to allow the tank to sit slightly closer to the trunk and expose the plastic wall of the trunk so the tank can be bolted to the trunk.

Now it is simply a matter of putting the tank on the bike, securing it with the straps to the hand holds and a bolt into the trunk to anchor it front to back, and routing the hose from the auxiliary tank to the newly installed fitting into the stock tank. (See first photo above)

This where the different hose sizes again comes into play. There isn’t much room for connectors and such, and the connectors I selected proved to be large enough to make things somewhat cramped. As you can see from photo number 1 above, the metal elbow fitting from the 90 degree change from 3/8 to ¼ hose is VERY CLOSE to the saddlebag, and I will be changing that before any long trips. I can see a big ugly scratch developing on the saddlebag from this connector rubbing on the saddlebag.

The red handle of the shut-off value is clearly shown in this photo. The idea is that at a gas stop, you fill both tanks, and close the value. You then use the bike’s gas gauge while you consume the gas in the stock tank (6.3 gal). When the stock tank is down between ¼ and reserve, you open this valve and let fuel flow from the auxiliary tank into the stock tank, and watch the gauge GO BACK TOWARD FULL. That should be fun to watch. My bench tests show it should take about 10 minutes with the ¼" hose. Then you use the stock fuel gauge to know when to stop and refill both tanks, remembering to turn the valve OFF so you can repeat the process on the next fuel load.

The quick disconnect allows the hose to be curled up and stashed under the seat when the tank is removed from the bike.

You can just barely see the fittings used at the inlet to eliminate any crimps in the hose.

That’s it. There are a couple of things I’d do differently, and will mostly likely be changing before a long trip. The most notable is the hose diameter step-down, and the fitting being right up next to the saddlebag.