Wondering if anyone's drilled an air hole in their fuel tank fill neck to increase the tank carry capacity yet?

[Keehn]

This is an OLD mod from the Chromeheads forum (which I did on my old R1200c) to increase the fuel tank capacity. The fuel neck in our bikes reaches FAR down into the tank, and, as a consequence, leaves a MASSIVE air pocket where gas can't occupy when you fill up.



The mod is to drill a small hole near the top of the fuel neck, like a 1/8" hole, to allow air to vent out while you're filling gas. However, this mod can sometimes result in overflowing the charcoal canister, thusly leading to a second mod of deleting the charcoal canister as well.

Also, while I typed this up, I headed over to Chromeheads to see if I could find the old post...and I couldn't. Maybe they took it down or it got lost when they transitioned to the new site???

Anyways, here's another person who did the mod so you can see what I'm talking about: https://motorcycleinfo.co.uk/r1200gs-fuel-tank-filler-neck-modification-fuel-filler-mod-indexfcd2/

If you do this, for the love of everything good in this world, PLEASE remove the filler neck from the gas tank BEFORE drilling the holes!!!!! We don't want to hear any KABLOOEY stories.

And yes, I 100% intend to do this mod to Alcina! I have been more than irritated that I'm unable to get the full listed tank capacity in her every time I'm at the gas station

Mike

 

[nielsm]

On my R18 Classic, I’m able to fill the gas all the way to the top with no mods. The neck is very different than that on my 2012 GSA & 2015 S1000R which look more like the above photo, but just taking the filler out a bit from the tank lets me fill those to the top too. If anything the neck on the R18 is more similar to the lack of a neck on my 1972 R75/5 Is the filler neck different on the fairing bikes to require this mod?

I’m typically 130 miles till the reserve light in aggressive back roads riding. I’ve conservatively aimed to refill about 20 miles after reserve. But, I’m only putting in about 3.5 gallons then so the reserve is more than 1 gallon remaining. My best tank thus far was 173 miles & I only put in 3.7 gallons, so the capacity hasn’t impacted me, as I typically want a break after 2 hours.

 

[Keehn]

On my R18 Classic, I’m able to fill the gas all the way to the top with no mods. The neck is very different than that on my 2012 GSA & 2015 S1000R which look more like the above photo, but just taking the filler out a bit from the tank lets me fill those to the top too. If anything the neck on the R18 is more similar to the lack of a neck on my 1972 R75/5 Is the filler neck different on the fairing bikes to require this mod?

I’m typically 130 miles till the reserve light in aggressive back roads riding. I’ve conservatively aimed to refill about 20 miles after reserve. But, I’m only putting in about 3.5 gallons then so the reserve is more than 1 gallon remaining. My best tank thus far was 173 miles & I only put in 3.7 gallons, so the capacity hasn’t impacted me, as I typically want a break after 2 hours.

Interesting. I have the transcontinental model, which I'm aware the classic and TC have different capacity tanks.

For mine, I'm only able to fill up to the bottom of the fill neck of the tank itself. I can jiggle the bike somewhat to "burp" the air bubbles out (which I also did on my old R1200c prior to the mod), but that only gets me a little more capacity.

Mike

 

[Noelpolar]

I can see some bald'n eyelash'less R18 owners in the future......

 

[nielsm]

Interesting. I have the transcontinental model, which I'm aware the classic and TC have different capacity tanks.

For mine, I'm only able to fill up to the bottom of the fill neck of the tank itself. I can jiggle the bike somewhat to "burp" the air bubbles out (which I also did on my old R1200c prior to the mod), but that only gets me a little more capacity.

Mike

Ultimately, i always fill to the same level on the bike as I track mileage with Fuelly across my fleet, so I know exactly what my typical mileage and thus range is and if it varies over time. Capacity is one part of the equation, but so is MPG. Combined, they define your range.

I expect the difference between the auto-shutoff fill amount and the “burped” amount is <1/8 gallon. If you get 40 MPG, that’s only about 5 miles more range, so not a significant impact.

As long as you can travel the distance between breaks or if you are in more remote parts of the world, between stations, it’s fine. Practically speaking, I’ve never felt I needed extra capacity on any of my bikes (including the tiny 2.1 gallon tank on my Vespa), but I live in a fairly populated part of the world & gas stations are rarely more than 20 miles apart. It’s far more common for me to stop for a break & not refill, than have range anxiety & feel the need to refill at every station I see.

 

[Keehn]

I can see some bald'n eyelash'less R18 owners in the future......

That's why you take the filler neck OFF the gas tank BEFORE you drill man!

And, for the record, I'm already bald. So, check that off the list...

Plus, for U.S.-based bikes, we have the charcoal canister that helps to capture any overflow vapors. In the R1200c, deleting the charcoal canister was necessary, as sometimes, gas spilled out of the overflow tube.

However, if you plumb the overflow tube safely under your bike AWAY from any hot objects (e.g. near your rear tire, below the muffler), you'll never have issues.

Mike

 

[Keehn]

Ultimately, i always fill to the same level on the bike as I track mileage with Fuelly across my fleet, so I know exactly what my typical mileage and thus range is and if it varies over time. Capacity is one part of the equation, but so is MPG. Combined, they define your range.

I expect the difference between the auto-shutoff fill amount and the “burped” amount is <1/8 gallon. If you get 40 MPG, that’s only about 5 miles more range, so not a significant impact.

As long as you can travel the distance between breaks or if you are in more remote parts of the world, between stations, it’s fine. Practically speaking, I’ve never felt I needed extra capacity on any of my bikes (including the tiny 2.1 gallon tank on my Vespa), but I live in a fairly populated part of the world & gas stations are rarely more than 20 miles apart. It’s far more common for me to stop for a break & not refill, than have range anxiety & feel the need to refill at every station I see.

I 100% get what you're saying, but for me, I'm not digging the fact that I'm not getting the advertised capacity in my tank when I fill up.

I'm not sure where you live, but here in Maryland, I like to ride Alicia out on the highways for long stretches at a time. And, if I can maximize my riding distance between fill ups (even if I don't have to right now), then all the better. I plan to eventually cross-country Alcina, where tank capacity will be critical (especially out west) and that's where this tank mod will make its money.

There's not a lot of...anything out in the Dakotas or Wyoming, so the less (or no) jerry cans I need to carry, the better.

Mike

 

[Ulrich]

I 100% get what you're saying, but for me, I'm not digging the fact that I'm not getting the advertised capacity in my tank when I fill up.

I'm not sure where you live, but here in Maryland, I like to ride Alicia out on the highways for long stretches at a time. And, if I can maximize my riding distance between fill ups (even if I don't have to right now), then all the better. I plan to eventually cross-country Alcina, where tank capacity will be critical (especially out west) and that's where this tank mod will make its money.

There's not a lot of...anything out in the Dakotas or Wyoming, so the less (or no) jerry cans I need to carry, the better.

Mike

I hear you there ... If I head out Eastern Oregon there are sometimes 150+ miles between tiny towns and other than that a whole lot of nothing. Asides that, I still have a coast-to-coast on my bucket list and tank capacity is very much on my mind ...

 

[nielsm]

I 100% get what you're saying, but for me, I'm not digging the fact that I'm not getting the advertised capacity in my tank when I fill up.

I'm not sure where you live, but here in Maryland, I like to ride Alicia out on the highways for long stretches at a time. And, if I can maximize my riding distance between fill ups (even if I don't have to right now), then all the better. I plan to eventually cross-country Alcina, where tank capacity will be critical (especially out west) and that's where this tank mod will make its money.

There's not a lot of...anything out in the Dakotas or Wyoming, so the less (or no) jerry cans I need to carry, the better.

Mike

You are getting the advertised capacity. The advertised capacity is defined as usable fuel capacity, not the absolute vessel capacity. Part of the tank is above the fill hole, so even with your mod, you wouldn't get the absolute vessel capacity. It might add a small % of a gallon, it's not going to turn your 6.3 gallon tank into 7 gallons.

I live in the southern NY so it's very populated & thus fuel is available with small spacing. Even riding to less populated areas on the east coast, I'm not worried. Out west in the US is probably the one area where you can worry about range. I believe the longest stretch in the lower 48 states with no other fuel available is about 168 miles between Ely & Tonopah Nevada. Alaska has the Dalton highway (240 miles between fuel) where I'd take my GS, not my R18 due to the dirt road nature. But for the most part, even the stock tank on the R18 Pure & Classic (4.2 gallons) works for almost all the longest stretches in the US (my distance to empty is 184 miles with my overall average 44 MPG). I mostly ride back roads fairly aggressively, so my MPG is probably lower than those who mostly cruise on highways. On Fuelly there are a couple R18B and their overall average is 45 MPG. If we assume 45 MPG for your TC with 6.3 gallon usable fuel capacity, your distance to empty is 283 miles, so you'd still have about 1/3 tank remaining after the longest stretch in the lower 48.

I track every single fueling on every bike & car I have, so I'm very confident in my expected range, typical, worst case & best case. If you are light on the throttle, you can improve your MPG. My absolute best tank, riding a bit of steady highway plus some back roads was 48.2 MPG which gives distance to empty on my Classic of 202 miles. My reserve light would have just come on with the longest stretch in Nevada. My worst tank was 39 MPG (first tank on the bike), so my distance to empty would have been 163. Carrying a small extra bit of fuel in a fuel canister for that long stretch can give more breathing room. I may carry some extra fuel in a portable collapsible bag like one from Giant Loop https://www.giantloopmoto.com/product/armadillo-bag-liquid-power-reservoir/ to have more peace of mind on those long stretches assuming my worst MPG. An extra gallon would give me range of 202-249 miles depending on how light I was on the throttle. The fuel bag is small enough to roll up & store in a saddlebag when not using & I'd only fill it for the long stretch as a backup. If I'm pessimistic, they have 2 & 3 gallon ones too.

 

[Keehn]

You are getting the advertised capacity. The advertised capacity is defined as usable fuel capacity, not the absolute vessel capacity. Part of the tank is above the fill hole, so even with your mod, you wouldn't get the absolute vessel capacity. It might add a small % of a gallon, it's not going to turn your 6.3 gallon tank into 7 gallons.

I live in the southern NY so it's very populated & thus fuel is available with small spacing. Even riding to less populated areas on the east coast, I'm not worried. Out west in the US is probably the one area where you can worry about range. I believe the longest stretch in the lower 48 states with no other fuel available is about 168 miles between Ely & Tonopah Nevada. Alaska has the Dalton highway (240 miles between fuel) where I'd take my GS, not my R18 due to the dirt road nature. But for the most part, even the stock tank on the R18 Pure & Classic (4.2 gallons) works for almost all the longest stretches in the US (my distance to empty is 184 miles with my overall average 44 MPG). I mostly ride back roads fairly aggressively, so my MPG is probably lower than those who mostly cruise on highways. On Fuelly there are a couple R18B and their overall average is 45 MPG. If we assume 45 MPG for your TC with 6.3 gallon usable fuel capacity, your distance to empty is 283 miles, so you'd still have about 1/3 tank remaining after the longest stretch in the lower 48.

I track every single fueling on every bike & car I have, so I'm very confident in my expected range, typical, worst case & best case. If you are light on the throttle, you can improve your MPG. My absolute best tank, riding a bit of steady highway plus some back roads was 48.2 MPG which gives distance to empty on my Classic of 202 miles. My reserve light would have just come on with the longest stretch in Nevada. My worst tank was 39 MPG (first tank on the bike), so my distance to empty would have been 163. Carrying a small extra bit of fuel in a fuel canister for that long stretch can give more breathing room. I may carry some extra fuel in a portable collapsible bag like one from Giant Loop https://www.giantloopmoto.com/product/armadillo-bag-liquid-power-reservoir/ to have more peace of mind on those long stretches assuming my worst MPG. An extra gallon would give me range of 202-249 miles depending on how light I was on the throttle. The fuel bag is small enough to roll up & store in a saddlebag when not using & I'd only fill it for the long stretch as a backup. If I'm pessimistic, they have 2 & 3 gallon ones too.

Nielsm, I like a challenge.

I'm currently working on wifey's 76' Honda CB500t, along with a couple other projects, so give me a little time. But, I'm gonna do the tank mod on Alcina.

Beforehand, I'll ride her down to the reserve tank light warning, with monitoring how many miles I put on post-reserve until I can fill her up to max capacity (as factory stock). Then I'll post my findings here. I'll likely make a new standalone post, but I'll link to it here.

So, more to follow.

Mike

 

[nielsm]

Nielsm, I like a challenge.

I'm currently working on wifey's 76' Honda CB500t, along with a couple other projects, so give me a little time. But, I'm gonna do the tank mod on Alcina.

Beforehand, I'll ride her down to the reserve tank light warning, with monitoring how many miles I put on post-reserve until I can fill her up to max capacity (as factory stock). Then I'll post my findings here. I'll likely make a new standalone post, but I'll link to it here.

So, more to follow.

Mike

I typically ride past the reserve every tank. Assuming the worst, I only expect 39 MPG (my worst tank) once I hit reserve (~1 gallon remaining) so I aim to refill within 20 miles. The most I’ve put in is 3.743 gallons into a 4.2 gallon tank, which is right where I’d expect it, assuming about 20 miles remaining range.

 

[Adrian R]

Insane, what r u nutz? I can fill my R18C all the way to the top, which I rarely do...and get plenty of miles from a full tank.

 

[bill12920]

This is an OLD mod from the Chromeheads forum (which I did on my old R1200c) to increase the fuel tank capacity. The fuel neck in our bikes reaches FAR down into the tank, and, as a consequence, leaves a MASSIVE air pocket where gas can't occupy when you fill up.

View attachment 10183

The mod is to drill a small hole near the top of the fuel neck, like a 1/8" hole, to allow air to vent out while you're filling gas. However, this mod can sometimes result in overflowing the charcoal canister, thusly leading to a second mod of deleting the charcoal canister as well.

Also, while I typed this up, I headed over to Chromeheads to see if I could find the old post...and I couldn't. Maybe they took it down or it got lost when they transitioned to the new site???

Anyways, here's another person who did the mod so you can see what I'm talking about: https://motorcycleinfo.co.uk/r1200gs-fuel-tank-filler-neck-modification-fuel-filler-mod-indexfcd2/

If you do this, for the love of everything good in this world, PLEASE remove the filler neck from the gas tank BEFORE drilling the holes!!!!! We don't want to hear any KABLOOEY stories.

And yes, I 100% intend to do this mod to Alcina! I have been more than irritated that I'm unable to get the full listed tank capacity in her every time I'm at the gas station

Mike

There's a reason they designed it the way they did. Ever see what happens to a boat tank (the red plastic ones) when sitting in the sun for a while? Park in the sun, your fuel is going to expand. Do this mod, and there's no place for it to go other than force a leak out at the weakest point in the system.

 

[Keehn]

So, it appears that BMW has...BMW'd its tank breather valve for the R18. Once upon a time, the R1200c tank breather valve was a simple analog device. However, after reviewing the microfiche, I'm getting the impression that even this valve is monitored by the DME as a sensor. However, I could be wrong, but absent anything else, I'm going with this hunch.



So, I need to figure out exactly where this breather valve resides on Alcina. That will have a significant impact on my movements with this project carrying forward.

I know that, like my old R1200c, the holes will need to be drilled on the right-hand side, so as to favor the left-hand kickstand. But now, the depth of the holes may be dictated by where the placement of the breather valve lies, rather than simply deleting the charcoal canister. If it's determined that the drill hole is only an inch or so higher than the bottom, then I'll CANEX (cancel exercise) and this thread can then serve as an AAR (After-Action Report).

Sidebar: I did a bench calibration of wifey's Honda CB500t carburetors. Turns out her float bowl fuel cut off tangs were letting too much fuel into the carb bowl, so I extended the float bowls to full extension, then bent the tangs so they were parallel with the bowl gaskets, like they should be. Tomorrow I adjust her valves.

Mike

 

[Keehn]

Okay, so an update...

I finally found some bandwidth to take Alcina out for a stroll and ride her tank down to reserve...for the excuse to fill her from reserve back to full. Here's my findings:


Reserve tank indicator kicked in at 42 miles, so 42 - 34 = 8 miles into reserve tank. I average 40.6 MPG. Back of napkin math, I'd guesstimate I dipped ~ 0.2 gallons into reserve, assuming 42 miles was the cutoff into reserve mark.

The owners manual for the Transcontinental states that my bike has approx. 6.3 gallons of usable fuel capacity, with approx. 1.1 gallons of fuel reserve.



Note that Alcina is on her side stand in this photo, and that the gas is slightly above the bottom inward section.



The grand total filled was 4.733 gallons, which, if I add the 0.2 I used in reserve, comes to 4.933 gallons.

Now, this is the part where I'm supposed to look stupid, but I'm still extremely frustrated, and I'll explain shortly. 4.933 gallons usable gallons + approx 1.1 reserve gallons = 6.033 gallons!

Seems like Alcina is holding the quantity of fuel that BMW advertised!

HOWEVER...

Not 15 miles down the road, the first fuel bar indicator is already gone! , (sorry, didn't get a pic at 80MPH on the highway!) and this has happened since DAY ONE!

But, and I think I should get a picture to better illustrate my point, but I'll try describing here, when you lean the R18 on the side stand, there's a crap-ton of empty volume left in the fuel tank above the bottom of the fill neck (picture an imaginary line running through the tank, touching the bottom of the fill neck and coming out the right-side of the bike for perspective). For anyone who's saying "tHe TaNk WiLl LeAk"...have you ever ridden like...I don't know...any other motorcycle NOT made by BMW? My wife's Honda doesn't have a fill neck stretching down into her tank, I know Harley Davidson sportster tanks are just as basic.

So long as there's enough room at the top of the tank for fuel vapor to escape, that's all that's necessary for safety.

Now, I say all that to also say that I might not be able to do this mod in the timeframe I was hoping after all...

Why? Whelp...notice something in the middle picture? Yeah, BMW got pretty and WELDED the fill neck to the fuel tank!

So, I would need to remove the tank from the bike, drain it, COMPLETELY disassemble it, and then VENT IT via a gas-safe ducted fan for a couple days at LEAST.

So...at this moment, BMW wins the battle. But mark my words......



Mike

 

[nielsm]

But, and I think I should get a picture to better illustrate my point, but I'll try describing here, when you lean the R18 on the side stand, there's a crap-ton of empty volume left in the fuel tank above the bottom of the fill neck (picture an imaginary line running through the tank, touching the bottom of the fill neck and coming out the right-side of the bike for perspective). For anyone who's saying "tHe TaNk WiLl LeAk"...have you ever ridden like...I don't know...any other motorcycle NOT made by BMW? My wife's Honda doesn't have a fill neck stretching down into her tank, I know Harley Davidson sportster tanks are just as basic.

I always fill my bikes with them vertical. If you only fill on the side stand, you won’t get the usable fuel volume, but a smaller capacity due to the empty volume you mention. This may be why you lose a bar on the fuel gauge quickly. I’ve never confirmed the delta in volume as I’ve never filled any bike I owned on the side stand, but could be worth seeing how much more fuel you get with it vertical.

 

[Keehn]

I always fill my bikes with them vertical. If you only fill on the side stand, you won’t get the usable fuel volume, but a smaller capacity due to the empty volume you mention. This may be why you lose a bar on the fuel gauge quickly. I’ve never confirmed the delta in volume as I’ve never filled any bike I owned on the side stand, but could be worth seeing how much more fuel you get with it vertical.

Nielsm,

That's how I normally fill; me on the saddle, and Alcina standing straight up. This go-around, I decided to side stand her and try to squeeze as much as I possibly could. In either position, my first fuel bar still blinks out WELL before I believe it should. It's just on this occasion that I was carefully monitoring the mileage it went down. I'll make a note next time as well when I fill up while vertical, if that makes any impact.

Mike