2018 FJR AUX Tank Plumbing

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travel_man

Greg Rice
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I bought a new 2018 FJR A model a month and a half ago and I spent a little time looking into how the best way to plumb a AUX tank in to the main tank. I read all of the posts here and other places how to drill the main tank and install a bulkhead fitting. I have done that process on many motorcycles ( mostly gold wings ) since 2004 and I always found it unnerving when I drilled a hole in a perfectly good gas tank. So I looked at other options like I had done on my 2018 Gold Wing and my 2019 GSA which is to tap into the gas tank vent system to draw gas from a AUX tank. It worked well on the Gold Wing and the GSA so why not the FJR.

I did some research and found the FJR has the same closed loop fuel system like all modern motorcycles and in theory it should work on the FJR.

I found some photos of the gas tank online that showed two small tubes coming out of the bottom left side of the gas tank. I did some more research and found one is for the vent to the gas tank and the other is the rain water drain from around the gas cap.

I rode over to Joe Green's house as he has a nice motorcycle lift so we could take a better look and do some testing to confirm what I had read.

We removed the gas tank and found the two metal tubes like in the photos and there was a rubber tube running from each and there was a t valve where the two rubber tubes were merged into one. I found this interesting as one of the metal tubes is for the gas tank vent which sucks air up into the gas tank and the other is a water drain that allows water to run down into the tube and out under the bike.

To confirm which metal tube is the gas tank vent we used a air compressor to blow air into both metal tubes. Once we had that figured out I ran my AUX tank fuel line to the front metal tube and removed the T valve and connected the rubber drain tube to the back metal tube for the water drain.

I temporally mounted my smaller GAS AUX tank ( 3.4 gallons ) for testing. I removed the passenger seat and the AUX tank fit nicely in that spot. 

The way this works is that as the engine pulls / pumps gas from the main tank it sucks air through the vent line. It is a very slow process. So instead of sucking air through the gas tank vent line it is now sucking gas. The AUX tank becomes the vent for the main gas tank.

So far I have ridden 500+ miles with this setup and filled the AUX tank 3 times ( I did not wait for the main tank to be empty ) and each time the AUX tank emptied be while the fuel gauge continued to show full.

I need more testing ( hopefully this coming weekend I will get to ride a couple thousand miles ) and I need to see how it works when it gets damn hot outside.

Greg-FJR-Aux3s.jpg
 

Greg-FJR-Aux2s.JPG


Greg-FJR-Aux1s.JPG


 

Canadian FJR

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In theory, if the aux tank was mounted higher it should transfer quicker wouldn't it?

Your timing is perfect, mine is on the lift and the aux tank is on my winter "to-do" list.

Canadian FJR

 

Kendoo

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This is why I wished you bought a FJR years ago.  Would have saved my nerves on the day I had to drill.  Hopefully it all works out.  Contemplating a Stagecoach run next month....will I see you there?

 

travel_man

Greg Rice
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In theory, if the aux tank was mounted higher it should transfer quicker wouldn't it?

Your timing is perfect, mine is on the lift and the aux tank is on my winter "to-do" list.

Canadian FJR
Yes, in theory it would need less sucking power. When I am done my AUX tank will be mounted a couple inches higher.

 

dcarver

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Intriguing idea, Greg. Always good to have new riders in the FJR hood, new ideas happen then. 

Keep us posted with your testing in hot weather. Theoretically  it should work fine. And no fittings to leak, aux fuel pump to quit... 

 

travel_man

Greg Rice
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This is why I wished you bought a FJR years ago.  Would have saved my nerves on the day I had to drill.  Hopefully it all works out.  Contemplating a Stagecoach run next month....will I see you there?
I am planning on attending Stagecoach and I have a hotel reservation, I hope to see you there.

This weekend I am planning a ride to the Isle Of Capri Casino where I screwed up in the IBR and buy that damn poker chip that cost me 19,000 points. ☹️

 

Canadian FJR

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Question:

On my other FJR, I drilled my tank.  I kept the aux tank off until the main tank was around a 1/4 full then I flipped the switch and watched the fuel bars climb.

If I leave the fuel cell off with this scenario, how will the main tank vent?

Canadian FJR

 

travel_man

Greg Rice
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Question:

On my other FJR, I drilled my tank.  I kept the aux tank off until the main tank was around a 1/4 full then I flipped the switch and watched the fuel bars climb.

If I leave the fuel cell off with this scenario, how will the main tank vent?

Canadian FJR
In my scenario you can NOT turn off a valve to the AUX tank as the AUX tank is now the vent and it needs to be open all the time. If you close the valve to the AUX tank eventually the bike will stall like it ran out of gas. I tested that on my 2018 Gold Wing and that is what happened.

 

FJRay

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Good idea unless it's a Californicator bike. On those the line runs to the carbon canister and then back to the engine. It would work if you disable the canister system but that would be against the law and Nobody would do that would they??? :punk:

 

travel_man

Greg Rice
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I rode a BBG ( 1650 miles & 1750 in 26 hours ) this weekend and the AUX tank plumbing worked great with no issues. At each gas stop the AUX tank was empty and my range was about 330 miles at a BBG pace with about a total of 9.8 gallons on board. One of the surprises I had after buying the 2018 FJR was how good of MPG's it gets.

 

Canadian FJR

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Ok, time for specifics.  Do I need to do anything different with the vent on the auxiliary tank?  My vent is simply coming off a nipple at the top of the tank.  My fill cap is flush, not a raised fill neck like yours.

Also, what kind of temps did you ride in?

Canadian FJR

 

James

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I'd thought about this years ago, but had already drilled my '04 tank. Haven't done the '15 yet, and this might be the way to go. Any thoughts on how the old problem solved by a "ballectomy" (tank over pressurizing) might be affected by this?

 

travel_man

Greg Rice
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Ok, time for specifics.  Do I need to do anything different with the vent on the auxiliary tank?  My vent is simply coming off a nipple at the top of the tank.  My fill cap is flush, not a raised fill neck like yours.

Also, what kind of temps did you ride in?

Canadian FJR
The temps ranged from 80 to 44 degrees. I guess I will have to wait until next year to test in hot weather.

All you need is a good vent on your AUX tank. The gas cap does not matter. I have a 1/4 inch inside diameter vent line on my AUX tank. A bigger one would not hurt.

 

travel_man

Greg Rice
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I'd thought about this years ago, but had already drilled my '04 tank. Haven't done the '15 yet, and this might be the way to go. Any thoughts on how the old problem solved by a "ballectomy" (tank over pressurizing) might be affected by this?
I think tank over pressurizing is possible in high temps. I have had it happen to my on my 2018 Gold Wing in 95+ temps. I think this happens when the heat causes gas expansion greater than how much gas the engine is using. Having a good vent system should help prevent this.

 

natehawk750

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So the AUX tank just vents to atmospheric pressure?

On my GS I had the AUX tank plumbed into the vent system but it was more of a closed loop system that's why I ask.

 

Brodie

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What kind of hose are you running from the Aux. tank to the main? I would think it would need to be a rather stiff wall to keep from collapsing when drawing gas. Also, with the Aux. tank much higher than the main, might there be a chance of a siphon occurring?

just a thought. 
 

Brodie

🧐

 

travel_man

Greg Rice
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What kind of hose are you running from the Aux. tank to the main? I would think it would need to be a rather stiff wall to keep from collapsing when drawing gas. Also, with the Aux. tank much higher than the main, might there be a chance of a siphon occurring?

just a thought. 
 

Brodie

🧐
I am using high end reinforced fuel line so it will not collapse. I am also using a reinforced vent line so it will not collapse.

I do not think there is any way for a siphon process to happen where fuel is pulled back into the AUX tank because there is no way for the main tank to get air other than through the vent line that I am using for the AUX tank. For a siphon process to happen the main tank would need a way to fill the space with air as gas was siphoned out.

I have over 60,000 miles on 3 different motorcycles with my AUX tank plumbed this way and only the Gold Wing had an issue in high heat, above 95 degrees because of all of the plastic around the bike and not enough air flowing over the engine and gas tank.

The FJR and the GSA bout have gas tank that are not covered in plastic and they are both metal gas tank which dissipates heat better than plastic gas tanks.

 
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