Fuel Filler Neck Modification, improved venting

[IMXMAN]

I searched and could not find a detailed description of this procedure so here is how I modified the fuel filler neck in order to provide improved tank filling.

Cautions and disclaimers:
I do not know if this will void your warranty or not.
Proceed at your own risk. After modification, be careful not to completely fill your tank, you should leave room for temperature expansion of the contents.
This is dangerous due to potential for ignition of gas fumes and possibility of property damage and personal injury or death.
Disconnect your battery and work in a well ventilated area. Do not allow sparks or other sources of fume ignition in the area.

The bike shown is a 2008 K1200S with the plastic style fuel filler neck. Early production years (2005-2006?) have metal filler necks and may require a different procedure.

With a torx driver remove the 2 screws holding the battery cover in place, slide cover forward and remove. Disconnect your battery. Place something non-conductive over the exposed battery terminals so that you don’t accidentally create a spark by laying a tool or a part between them.




With a torx driver remove the 6 screws holding the gas filler cap in place and remove the cap.




Remove the seat.

Remove the 6 torx screws holding the 2 gas tank decorative side panels in place, there are 3 screws per side. Leave the side panels in place; you just need to be able to wiggle them enough to remove the center decorative panel that runs from the battery cover down to the seat. Remove the center decorative panel.





The plastic fuel filler neck is now ready to be removed. However before pulling it out understand that there are interior tank items attached to it. On the left side of the neck you will see a small hole where the gas cap sits when closed. This hole is connected to a vent hose inside the tank.




On the right side of the neck is a metal bail which suspends the fuel level sender. The fuel level sender is delicate, long and “S” shaped. Pay attention to how the fuel sender is positioned because you need to replicate this to reinstall it. Carefully tilt the fuel filler neck up from the left side first, allowing the fuel sender to hang below the tank opening and then you can pull the assembly out several inches to work on it. There is no need to disconnect the fuel vent hose.









Once the top of the fuel sender strip is exposed, you can simply unhook it from the metal bail of the fuel filler neck and let it sit partially out of the tank. No need to completely remove the fuel sender strip from the tank.
There is a rubber gasket under the filler neck, be sure this does not fall into the tank.








Put a clean rag over the gas tank opening to help control fumes, lessen possibility of ignition and to keep debris out of tank.

Prepare a drill with a small drill bit, I used a 9/64” size bit. Caution, an electric or battery powered drill motor will make sparks and can ignite gas fumes. Be sure the area is well ventilated or use a hand or air-powered drill.

Carefully drill holes around the perimeter of the neck. I drilled 5 holes in the neck approximately where the filler funnel shape from above turns into more of a tube shape. The plastic is soft and will drill very easily, do not press hard on your drill. Clean away any plastic shavings left over. After testing this out, five 9/64” holes works very well, you may be able to work with fewer holes if you like.










Hook the fuel sender strip back on the metal bail.





Reinserting is the trickiest part: As mentioned earlier the sender is “S” shaped and the lowest side of the sender sits into the lower left side of the tank while the upper portion of the sender hangs over the right side of the tank. Inside the tank is the fuel pump assembly which you will need to work the sender strip first over and then around. To install into tank, again tilt the left side of the fuel filler up, allowing the metal hanger to point down toward the tank opening. Carefully feed the bottom of the fuel sender strip over to the left side of the tank, above the fuel pump, and then lower down the sender down the left side of the tank past the fuel pump assembly. As you feed the sender the last little bit into the tank, make sure the tank opening rubber gasket is resting correctly with the internal lip properly seated around the top of the tank opening. Feed the expansion vent hose into the tank and tilt the fuel filler tube back to level and resting on top of the rubber gasket. Make sure the 6 screw holes are aligned and that the hose vent hole indicates proper positioning by still being located on the left side.

Remaining assembly is reverse of removal.

[BillA]

Nice job Xave, and nicely documented. I do have one question: How did you decide to make the hole 9/64 instead of 8/64?

Bill Eh

[Pirate]

Excellent report and documentation..

I do have a question that may or may not showcase my ignorance... You say the procedure will "improved tank filling"... As I've never noticed any problem with tank filling on this bike or any bike I've ever owned... HOW exactly does it improve filling? Splain' it to me like I'm a chimp...

[Loggiebone]

Originally Posted by Pirate

Excellent report and documentation..

I do have a question that may or may not showcase my ignorance... You say the procedure will "improved tank filling"... As I've never noticed any problem with tank filling on this bike or any bike I've ever owned... HOW exactly does it improve filling? Splain' it to me like I'm a chimp...

There's an air pocket at the top that won't let the tank be as filled as it could. This hole allows air to escape allowing more room for bananas for the chip...

Tim and others did that very thing a long time ago...

[Pirate]

Interesting.. Thx, ancient dude. Never experienced this phenomenon.. ever..

Originally Posted by Loggiebone

There's an air pocket at the top that won't let the tank be as filled as it could ...

[IMXMAN]

Originally Posted by BillA

How did you decide to make the hole 9/64 instead of 8/64?

Bill,
I picked 9/64" mainly because it is about the size of the existing factory expansion vent hole. I considered a larger hole but thought that may allow splashing while filling. A series of smaller holes might still work too.
The main thing is to allow enough air gap venting so that the gas pump can evenly fill in behind the plastic tube without needing to stop and wait for the pressure to equalize.
I also thought putting several holes around the perimeter will allow higher fuel levels whether the bike is on centerstand or the sidestand, and to take sloshing while filling out of the equation.
So far so good, I can now fuel quickly right up to the level of the holes. No bumping of the gas pump required - eh.

Pirate,
As Loggiebone explained there is an air gap at the top of the tank that is effectively created by the unmodified fuel filler tube extending down into the tank. This is probably a BMW design decision to allow room for fuel expansion. Several people have complained (including me) that filling the last inch or two of the tank is a frustrating process of bumping the gas pump and being careful not to splash fuel back into one's face. Adding the holes makes that filling process much cleaner, quicker and simply allows more fuel to enter the tank.

It is possible to drill the holes higher than where I did, but I intentionally chose to leave some room for an expansion air gap. Additionally I was not sure how higher holes would work with the gas cap sealing mechanism. The location where I drilled the holes is clearly below the bottom of the gas cap.

[cabnfvr]

Excellent. I did this a couple of years back to our S ,and I did use an electric drill. I had a WET towel packed into the tank opening and a damp towel wrapped around the drill. I also had a copy of our insurance in a safe place and was wearing running shoes.

Seriously, I never posted it because I didn't want to say "don't do this!". It does make fillig much easier, as you can now see the fuel as it fills. It also holds a few 10ths more fuel and some days that matters.

[George_in_KG]

I also copied Tim and made the mod to my KS a couple of years ago. It helps prevent splashing of gas on the paint as the tank approaches full. Air wants out as the gas is going in. Air bubbles = gas splash before the mod.

Should this be called the Tim Hole?

[skapan]

Maybe I'll heat up a nail with the propane torch and melt a few holes in the neck. Won't have to take it apart, but then again it might self-disassemble if it catches fire! Maybe I'll just leave it alone for now. It really could have been better from the factory.

[Kneedragger]

Originally Posted by BillA

Nice job Xave, and nicely documented. I do have one question: How did you decide to make the hole 9/64 instead of 8/64?

Bill Eh

They don't make drill bits in 8/64... the closest you can get is 1/8...

[Cambridge K]

I - like george in kg did this years ago - BUT go larger in holes & more holes - saves time gasing up - no rock & rolling to get the air out & gas in. I've gotten 5.077 gas in my K12S tank with 2 miles left on the computer. I have the metal filler neck - I started out drilling small holes & went larger - I have 4 to 5 1/2 holes in around the neck - Looking at the plastic neck - you have no bottom / it's open- the metal filler neck has a bottom with a large hole at the bottom. Old K's bike had a flapper plate at the bottom of the filler neck.
So larger & more holes in the neck - is the way to go, gas & go - no waiting & rock /rolling the bike to get the air out of the tank.

[EricM]

Originally Posted by Pirate

Interesting.. Thx, ancient dude. Never experienced this phenomenon.. ever..

Put your reading glasses on next time you gas up!

[woolf]

has any one done this to an HP2 SPORT or R1200RT ?????????? with the red rubber ?

[edzt]

Originally Posted by woolf

has any one done this to an HP2 SPORT or R1200RT ?????????? with the red rubber ?

Done it to my Megamoto if that counts..........Good for an extra 15 to 20 miles per tankful

[McWideglide]

I don't have an 8/64 either. I found a 4/32 though. That should work just fine.

[skapan]

Yes, I have 2/16 but it looks bigger than 4/32, maybe 8/64 is really the way to go.