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The bike is a 1998/99 Honda CBR 600F. The drain tube seems to be corroded inside the fuel tank, based upon 2 symptoms:

  • Filling the tank more than 3/4 full causes petrol to drain from the drain tube
  • Water which collects around the fuel cap (eg, during rain) dribbles into the tank, rather than escaping down the drain tube

I've been advised that the correct fix is to replace the entire fuel tank.

Whilst searching for a fuel tank to buy, I noticed that individual drain tubes and breather tubes are available, and I wondered:

Maybe these tubes are replaceable without replacing the entire tank?

Trouble is, as far as I can tell, these tubes are inside the fuel tank, and therefore impossible to get to. Or are they?

Example: see parts 15 & 16 in this schematic

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    Where is @DucatiKiller when you need him! With my limited experience with bikes, I would bet the you will need to replace the tank. The reason I'm saying this is, what you are looking at changing is on the outside of the tank, while the rusted piece is located inside the tank (it's probably what the tubes connect to). Changing out the tubes probably would not give you any relief of the symptoms. – Pᴀᴜʟsᴛᴇʀ2 Feb 20 '15 at 20:50
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    @DucatiKiller ... I know very little about bikes beyond regular mechanical things. I figure I'd leave it to an expert as you've proven yourself to be ... even though I did call it! ;-) – Pᴀᴜʟsᴛᴇʀ2 Feb 26 '15 at 1:29
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Interesting issue

IF, the internal tubes have corroded within the tank that would be relatively serious. The interesting piece is, how would they corrode. As far as I know, almost ALL the fuel tanks on modern bikes use copper for this overflow. It runs from the lip above the filler point, down through the tank to a nipple on the underside of the tank (or in the case of Kawasaki's) to a nipple under the front of the seat on the top side of the tank towards the rear.

Here is a standard Honda Fuel Injected tank design cutaway. This is for a CBR, post '06. enter image description here

You can see the two tubes running through the tank. The larger one is the overflow and it's made of a copper and nickel alloy.

The question is, how can it corrode?

It has some of the best general resistance to aqueous corrosion of most of the alloys. It also, when used in a fuel tank, has an epoxy coating....as does the rest of the fuel tank.

Theory

After thinking about this for a minute, the idea that the tank coating has been stripped out of the tank keeps recurring to me. Those tubes just don't corrode with the epoxy lining, nor does the tank. It's steel and would turn into a shell of rust and post-apocalyptic dysphoria pretty quick. Imagine hitting the dew point everyday with a low fuel level and lots of atmosphere inside the tank. Water droplets, tiny ones, form on the inner tank surface and then you get rust.

Therefore, if I'm right, the tank has been stripped using that standard commendation, with a water/acid mixture. It removed the epoxy coating off the copper. The copper became exposed to oxygen and began to....that's right...oxidize and degrade over time.

If I am correct, there will be rust on the inner tank surface as well. If there is no rust on the inner tank surface then there is a good chance I'm incorrect on how this happened.

Solution

Buy a new tank. You can't plug those nipples. If the line internally is broken and gas from inside the tank can exit that broken copper line, you fuel is essentially exposed to the atmosphere and whatever sparks, fire or any other ignition source the rest of the world is exposed to. Think static electricity here, with a low amount of fuel and lots of airspace in the tank. It would create a might fine explosion worthy of any virul youtube video. The exit of that line is near an exhaust pipe, right?

Throw it way, get a used one on Ebay from a seller with a good rep. Sorry for the bad news. 99% non fixable.

  • Would love to know where you found that cutaway picture! – Stewart Feb 27 '15 at 8:50
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    I think I got this from a Honda website in Japan. Can't remember since it's been a year. Sorry I missed this until just now. – DucatiKiller Mar 18 '16 at 20:04
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I believe you are correct in saying the tubes are inside the tank. What the manufacturers did was ran molded tubing through the tank and it sounds like those tubes in your case have rusted and corroded.

What I would suggest in your situation is just plugging the inlet for the overflow by the filler, and the overflow outlet which comes off the tank. You may be able to use some rubber nipples to achieve this.

This will allow you fill your fuel tank till it's full, and keep it in there. The issue now, however, will be that if you overfill your tank the fuel will run out over the top.

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    And I would need to take care about water which collects around the fuel cap, to avoid water in the fuel tank. – Stewart Feb 24 '15 at 7:36
  • Correct. Can you provide a picture of the tank? Perhaps an top view and profile view? – gh0st Mar 24 '15 at 4:20
  • I've taken @DucatiKiller's advice, and bought a new tank. You really can't see much of the internal drain tubes. On the old tank I was able to feel a little bit with my fingers after I'd emptied it, but without opening her up with a tin opener, there's no way to really see what's going on in there. – Stewart Mar 24 '15 at 5:03
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Can be fixed, You can replace the breather pipe, ie video: https://www.youtube.com/watch?v=zFej6OKdt4k , do it at your own risk, tank need to be clean

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