2018 FJR AUX Tank Plumbing

[dem]

I had a vacuum draw aux tank on my old BMW, and had issues with it randomly not draining. Usually rides starting out at <40F, then riding into 80-110F (ie, california desert/death valley/etc.) And yes, I added a double vent and even removed the tip-over blocker.

This was very disheartening as I couldn't trust the tank. I ended up carrying a siphon kit just in case. I think I'll be going gravity or pump for the FJR.

 

[travel_man]

I rode another 800 miles last night riding back to south Florida so now 2500+ miles and everything has worked great.

 

[fljab]

<snip>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.

Greg, great write up, butt I want to clarify this picture.  The blue line is going to your aux tank?  And the tee is connected to what on each side?  Plus, we're looking to the front of the bike in this pic?

I've got to plump my new bike for aux and I like this idea.  I'm very interested to see how it works in hot weather.

 

[travel_man]

Greg, great write up, butt I want to clarify this picture.  The blue line is going to your aux tank?  And the tee is connected to what on each side?  Plus, we're looking to the front of the bike in this pic?

I've got to plump my new bike for aux and I like this idea.  I'm very interested to see how it works in hot weather.

The blue line is my AUX tank fuel line connected to the gas tank vent. The black / gray line is the gas cap water drain line.

If you was sitting on the FJR the two tubes coming out of the gas tank are in the back left corner of the gas tank. The one my blue aux tank fuel line is connected to is in the front of the two tubes.

Please remember I have not yet tested this setup in HOT temperatures. 

 

[dcarver]

Please remember I have not yet tested this setup in HOT temperatures. 

One would results are predictable. IF both tanks are too full, AND gas expansion due to temperature exceeds engine fuel consumption, overflow will occur.

 

[RossKean]

Even if not so full that expansion equals overflow, there is a fair chance that the induced vacuum in the main tank due to fuel consumption could just allow the gas to boil. Or at least have enough vapor pressure so it doesn't draw easily from the auxiliary tank.  If that happens,  you might have to stop and do a manual transfer.  Won't know until you try.  

I like the no-drill approach.  

 

[travel_man]

Even if not so full that expansion equals overflow, there is a fair chance that the induced vacuum in the main tank due to fuel consumption could just allow the gas to boil. Or at least have enough vapor pressure so it doesn't draw easily from the auxiliary tank.  If that happens,  you might have to stop and do a manual transfer.  Won't know until you try.  

I like the no-drill approach.  

I think worse case scenario would be you would have to open the main tank gas cap and release any pressure. This happened a couple times on my 2018 Gold Wing. Since the Gold Wing had a screw on gas cap I could just loosen it while riding and everything would be fine.

Maybe I will need to replace the FJR gas cap with a screw on one also as a precaution.

 

[Fred W]

Very cool idea.   Even better that it seems to work well.
 

It was briefly mentioned earlier in this thread as the “tip over blocker”, but were you aware that there is a check valve in line with the vent line located inside the Gas cap?  Inside the cap assembly there are two parallel vent paths.  One has a small metal ball fit into it that is a gravity operated check valve.  The other path has some sort of restrictive filter media.  
 

Normally the check valve is open to vacuum, but when you drop the bike it’s supposed to reduce the gas spillage out the vent pipe. Some of us removed those balls to prevent excess tank pressurization from fuel boiling. I was just thinking that the ball may restrict your liquid fuel transfer somewhat and you may want to get rid of it for better flow at low vacuum. It certainly isn’t doing anything for you when you have your aux tank connected.

 

[travel_man]

Very cool idea.   Even better that it seems to work well.
 

It was briefly mentioned earlier in this thread as the “tip over blocker”, but were you aware that there is a check valve in line with the vent line located inside the Gas cap?  Inside the cap assembly there are two parallel vent paths.  One has a small metal ball fit into it that is a gravity operated check valve.  The other path has some sort of restrictive filter media.  
 

Normally the check valve is open to vacuum, but when you drop the bike it’s supposed to reduce the gas spillage out the vent pipe. Some of us removed those balls to prevent excess tank pressurization from fuel boiling. I was just thinking that the ball may restrict your liquid fuel transfer somewhat and you may want to get rid of it for better flow at low vacuum. It certainly isn’t doing anything for you when you have your aux tank connected.

The BMW's also had a little tip over ball also that most of us removed. I plan on removing the ball one it gets a little warmer out and see what the effect will be.

 

[natehawk750]

I'm guessing everything is still operating properly with this setup? I might be plugging my tank and switching to this method soon.

 

[travel_man]

I'm guessing everything is still operating properly with this setup? I might be plugging my tank and switching to this method soon.

Yes, everything is working great so far. I have around 8,000 miles on the setup now.

 

[natehawk750]

Awesome! Thanks Greg.

 

[James]

It's kinda looking like it's time for me to figure out the difference in mounting from the '04 to the '15 and back up this test. I have a screw on filler cap I can move over from the "04 as well (pirates lair), but it wasn't as rain proof as I wanted. Might be easier to remove the tip over ball and keep the stock cap while it's new enough to come apart.

 

[travel_man]

I just another BBG over New Years Eve and no issues with the AUX draining. So far no drilling or modifications except to replace the vent hose with the AUX tank fuel line.

 

[Brodie]

Greg,

I am wondering how the vent is set up on the AUX tank. Do you have a puke canister to catch any fuel due to heat expansion? And if so, is there any way to reclaim it once things cool back down or when you start riding and drawing from the AUX tank after a few miles?

Brodie

 

[Wistrick]

Greg,

I am wondering how the vent is set up on the AUX tank. Do you have a puke canister to catch any fuel due to heat expansion? And if so, is there any way to reclaim it once things cool back down or when you start riding and drawing from the AUX tank after a few miles?

Brodie

unless im thinking about this wrong with this setup the aux tank is acting like a big catch can sucking fuel though the vent line...????

Expansion Tank

 

[Canadian FJR]

What size fuel - 5/16 (7.9mm) ??

——————

Also, I found these comments on the IB forum;

When both tanks are full and you ride away from the gas station the fuel is pumped out of the bike tank by the fuel pump. That sucks fuel from the aux straight into the bike tank litre for litre. At the same time air is drawn (litre for litre) into the aux vent line from outside. Once the aux is empty the bike tank starts drawing in air straight through the aux.The filling procedure is strict. Starting with the aux empty (it was empty in your shed) first fill the bike tank and put the cap on. Fill the aux and put the cap on. Do not open the bike tank unless you are positive the aux is empty - otherwise fuel will pour out the moment you open the cap. Do not fill the aux unless you are positive the bike tank is full. Otherwise you may create a vapour lock as there is a big bubble of air at the top of the bike tank. That air can't get out and the aux fuel can't easily get in. If the bike seems to be starved of fuel out on the road when you know you have gallons on board this is the likely cause. Carefully open the bike cap and you will hear air hissing. Wait a bit and the fuel from the aux will start to flow and fill the bike tank to the top. Cap it before it overflows.
 

I can see situations where I’d just fill one or the other tank without filling the other.

Canadian FJR

 

[travel_man]

Greg,

I am wondering how the vent is set up on the AUX tank. Do you have a puke canister to catch any fuel due to heat expansion? And if so, is there any way to reclaim it once things cool back down or when you start riding and drawing from the AUX tank after a few miles?

Brodie

Brodie,

No, I do not have a puke tank. Just the normal vent line.

 

[travel_man]

unless im thinking about this wrong with this setup the aux tank is acting like a big catch can sucking fuel though the vent line...????

Expansion Tank

That is correct. BMW riders have been using this method for many years.

 

[travel_man]

What size fuel - 5/16 (7.9mm) ??

——————

Also, I found these comments on the IB forum;

When both tanks are full and you ride away from the gas station the fuel is pumped out of the bike tank by the fuel pump. That sucks fuel from the aux straight into the bike tank litre for litre. At the same time air is drawn (litre for litre) into the aux vent line from outside. Once the aux is empty the bike tank starts drawing in air straight through the aux.The filling procedure is strict. Starting with the aux empty (it was empty in your shed) first fill the bike tank and put the cap on. Fill the aux and put the cap on. Do not open the bike tank unless you are positive the aux is empty - otherwise fuel will pour out the moment you open the cap. Do not fill the aux unless you are positive the bike tank is full. Otherwise you may create a vapour lock as there is a big bubble of air at the top of the bike tank. That air can't get out and the aux fuel can't easily get in. If the bike seems to be starved of fuel out on the road when you know you have gallons on board this is the likely cause. Carefully open the bike cap and you will hear air hissing. Wait a bit and the fuel from the aux will start to flow and fill the bike tank to the top. Cap it before it overflows.
 

I can see situations where I’d just fill one or the other tank without filling the other.

Canadian FJR

What I have found on the FJR is that if you are only going to fill one tank the best one is the main tank and NOT the AUX tank.