Best way to drill fuel neck to pack the tank?

[Oxide]

I have read various places that drilling a hole or cutting slot in the top of the fuel tank filler neck will allow you to much more quickly pack the tank to the top. I read on one of the MT forums that a guy used a Dremel grinding wheel to cut a small slot at the very top of the neck, I think I will use this method but wanted to ask if anyone has had first-hand experience with this or another method. It seems to me if I put a small bit of shop rag in the neck I can keep stuff from falling in the tank and if I cut into the rotation direction all the chips will go on the rag and not the tank. Probably best to take the tank off to remove the fuel pump so I can make sure all the chips are out. Thoughts?

Also does anyone know why there are two vent lines? I found the one with a white paint ring goes to the gas cap vent and the other empties into the top of the tank.

For reference, if you haven't looked into this before...

I slowly packed the tank today in the garage to see at what point the gas would come out of the vent and to my surprise it never did. I filled it to within 3/8ths of an inch of the top - so much that when I closed the lid it pushed some gas out. It never came out of the vent line. I got about 3/4 of a gallon extra from the bottom of the neck to the top. I then blew a small bit of shop air through the bottom of the vent line and heard it hiss, not bubble, at the neck. So I know wherever the vent opening is it at the very, very top of the tank.

 

[Oxide]

Alright so I got this done today. Took the tank off, removed the fuel pump and cleared out all the gas. I stuffed a rag in the top of the neck and held one on the back side of where I was cutting. Went very straight forward. I used a worn dermel cutting wheel so I would have a wheel with a smaller diameter. Wiped out the neck and inside really well and put her back together.

Unfortunately I scuffed the top ring a bit with the dremel chuck, but it's below the sealing surface so it's just cosmetic. I would suggest putting tape down to keep that from happening.

For reference I got 156 miles on the packed tank before I hit reserve. (120-130 normally; 35-37MPG is my norm) I went an additional 14 miles home to make it 170 even before emptying the tank. I would guess I pulled (& spilled) about 3 liters of gas out of the tank. I think I could have burned 2 of the 3 liters before getting to the level the pump couldn't get anymore fuel.

When I filled her back up with gas she took just shy of 5 gallons. So I would say the advertised 4.8 gallons is referring to absolute volume, not the recommended fill amount.

Also for anyone that was curious one vent line goes to the gas cap and the other to a hole under the rubber surrounding the gas neck on the left (to drain spilled fuel around the neck).

 

[packnrat]

much easier way for any used gasoline tank.

first have the bike on a flat lever surface.
second fill the tank up to the rim.
use a long drill bit and drill 4, 1/4 inch holes all around just below the top of the tank. keep the fuel level up.
this allows the air surge space to be used as added fuel area.
but when you fill to this point do not park and let the bike sit. as it will come out the vent hose. fill up and ride.

BUT KEEP the drill bit working end UNDER the level of the fuel.

liquid gasoline does not burn. gasoline vapors will very easily.

the liquid gasoline you are drilling in will help keep the hot parts cold.
DO NOT drill these holes on a used empty tank. and if any fuel in the bottom of the tank....you have your life and fire insurance paid up?

 

[Jboat]

 

[Klurejr]

This is a very interesting idea......

 

[Oxide]

Just got 204 miles out of a tank without running dry. Filled up with 5.1 gallons; not sure how I didn't get the full 5 gallons out of my jerry can when I first drilled the tank. Does gas really expand that much when it warms up?

 

[Klurejr]

I used to be able to get about 250 miles per tank when my fz1 was younger, I am above 120k miles on it now and even with a recent spark plug change the miles per tank is down. My tank did take some damage when a car knocked it over in a parking lot, so that has dropped the total amount of fuel I can put in it a bit.