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Discussion Starter #1
In addition to my Hexhead GS, I have an oilhead 1100RT. When the 1150RT came out, it had a much deeper filler neck which kept the tank capacity to just 6.6 gallons instead of the 7.1 that the 1100 had. It was an easy swap to put the filler neck from the 1100 in the 1150, and presto . . . an extra half gallon fit in the tank.

Has anyone experimented with changing the filler neck inside the fuel tank on the hexhead GS models to something shorter in order to maximize fuel capacity and, if so, what fits?
 

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If t a 2004 - 2007 Hexhead no need to change the filler neck simply drill a 5/16 +/- hole in the existing filler neck to let the air vent out.

I suggest doing at least one hole at the 3 o'clock position so if filling on the side stand the vent hole will be at the high side of the bike.

If you take the gas cap off you can pull the filler neck out of the tank enough to get rag around it and then shove a few paper towels inside the filler neck to contain the metal chips. Once drilled use a vacuum to suck out the chips and carefully unwrap the rag. Reassemble and you done. Just did the 2006 GSA filler neck on Sunday.

The 2009+ bikes have a different filler (second pic) and have two vented areas (as seen in the right side of the picture). I have not puled these fuel caps to see if these two vents extend down into the tank. If they do cutting them off would accomplish the same as drilling the metal filler neck.

A word of caution if you do this and fill the tank to the top if the bike sets in the heat the fuel expands and it will drip out of the overflow hose in into the evap canister flooding it or if you are like me and remove these Kalifornia only devises it will drip out of the vent hose onto the ground. This is not good if you have an asphalt driveway or if you park in you garage.

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Excellent answer. Thank you. Another winter project.

Just one question. You said a 5/16" hole. But how far down from the top flange should the hole be drilled? Or is it a matter of how much safety margin I want when refilling? If you make it too low, one can always drill a second higher hole. Would this be correct?
 

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Excellent answer. Thank you. Another winter project.

Just one question. You said a 5/16" hole. But how far down from the top flange should the hole be drilled? Or is it a matter of how much safety margin I want when refilling? If you make it too low, one can always drill a second higher hole. Would this be correct?
I drill it up as high as possibly which works to about 1/2" down from the top. Once you get things apart its obvious how far up you can realistically drill. More holes won't hurt but they definitely are not needed.
 
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