Fuel tank leaking: ideas?

Hi,
sorry for the IT topic on Friday evening.
My GS500 is leaking fuel from the "water drain hose" (as it is called in
the Haynes). I've done 100 miles with 16 litres (which means I've lost
at least 6 litres along the way). I've removed the tank and checked the
connection, it looks OK. I cannot see an obvious reason.
I have no idea of how a tank is made... do you have any suggestions on
why it should leak? I don't notice it when I drive, but now a colleague
just phoned me from the garage telling me that there is a patch of fuel
under my bike.
Apparently, it leaks more when the tank is nearly full, then it slows down
(but it keeps leaking).
It has been going on like that for a week now... Initially I thought I
had overfilled but now it looks like there is another reason.

Thanks,
F

 

Not unknown for water to sit right in the lower reaches of the tank and
eventually rust through the metal. I had it on a 5 year old Suzuki GS500
and it only finally blew when we filled the tank right up. Try a bit of
gentle prodding with a screwdriver as the paint may mask the problem,
but still allow fuel to seep out.

Steve

 

I know where the leak is coming from:
http://i73.photobucket.com/albums/i207/DigitalAnarchy/tubesbottom.jpg
it leaks from the open hose, the largest one (the shortest, too, in this
picture).
I followed it and it ends at the bottom of the tank, and everything looks
OK up to there.
Sometimes I see a drop falling, maybe one every two or three seconds.
Sometimes nothing.
Sometimes I park and when I go back I find fuel around. Sometimes it's
completely dry. In one week I havent' been able to find a pattern, I thought
it was fuel left around from overfilling but now it started again (and
moreover it must have been 6 litres or more in 1 week).

F

 

OK I think I need a lecture on the structure of fuel tanks... Do you have
a picture of a cross section somewhere?

Thanks!

F

 

Ahem... no idea sorry... It's not said in the Haynes manual, is there a
way I can tell from the outside? (it's a 2001 GS500).

F

 

Thanks! This is quite useful indeed.
This is the bottom of the tank:
http://www.gs-500.info/images/e/e9/Tankhahn2.jpg
It's not shown in this picture, but there is a hose connected to the
blue thinghy in front of the petcock. This hose then goes down to the
bottom of the bike, and this is where the fuel is coming from. In the text
it's called "overflow", I think.

F

 

The water drain pipe takes water away from the cavity around the fuel
filler. Are you sure that you have the pipes correctly connected ?.
If fuel is getting into that pipe you probably have corrosion.

 

Oh yes. Known weak point on old pre-Diversion Yamaha XJ900s, for
example.

 

Hello all,

Antony E' pit biatch here !

Craws out from behind bush to say,

Check that the water drain hose (from under the tank cap ) has not
become detached and the open end (or a leaky end),
is now sitting in the fuel inside the tank.
As the pressure builds up inside the tank, it forces fuel down the
pipe until it syphon's out, all on it's own!

Ducati's do the same if you forget to connect said pipe!

 

Pressure building up... this rings a bell... I've fitted a magnetic
tank bag, maybe it's blocking the air from outside? I'll check tomorrow.
But how do I check if the there is an open end /inside/ the tank? Do I
have to remove all the fuel and inspect it from the top?

Thanks,
F

 

As was mentioned above, this outlet drains the rainwater and
spilled/overflowing petrol from the recessed area under the
petrol filler/cap; like an overflow in a toilet cistern, it has no
connection to anything, it just runs through the inside of the tank to a
small hole at the top of the tank, with the tank removed you can look
through the hole forward and to the left of the filler hole and see
daylight at the bottom of it (with the drain hose removed) through to and
out of the (blue) painted outlet.

It is a remote possibility given the amount of petrol involved that the
internal pipe running through the tank from top to bottom has somehow
deteriorated. I've had a few of these and never seen that particular
failure, if that's the case then replacement seems inevitable.

 

First of all thank you for the suggestions.
I removed the tank and went through the whole system, inspected dissected
selected, and unbended the hose somewhere under the carburettors. It started
pissing happily half a gallon of petrol and then it stopped, more or less half
way of the tank (instead of going drop by drop for a few days).
So my guess is: there is a problem with the water drain hose from under the
tank cap. No, it's not detached so I guess it's damaged somewhere in the
middle. I was not able to see nor reach with my fingers any damaged area,
I think I have to find a small mirror from a dentist (do you have a better
idea?). It looks like a solid thing, not plastic hose.

Now, assuming this is the problem, do you have an idea of how you fix this?

Thank you!

F

 

Tool shops will sell you a mirror-onna-stick: very useful.

 

Costco currently have a set of magnet-, mirror- and
flexi-light-thingy-onna-stick, with lots of attachments and widgits to
allow you to use them in different combinations, in a nice little zip-up
case. I'd get one, if I didn't already have the magnet and mirror.

 

http://www.costco.co.uk/

But I don't think that's what you meant.

 

Costco don't do online shopping. You'll have to go to the shop yourself.
Oh, and you need to be a member.

 

http://www.screwfix.com/prods/64760...ent-Tools-Magnetic-Telescopic-Plumbers-Mirror
?

 

Was my detailed description not sufficient?

Tell you what: if I find myself in there in the near future, I'll get
all the details, take a photo, stick it up on the web, then send you the
link. Okay?

Hang on, though: is there a Costco near you? Are you a member?

 

You're not really like to pay the membership fee just to buy a souped-up
mirror-onna-stick anyway then, so my original link contained all the
information you needed to make your decision.

 

We've all got them up here, 'cos we're all well dodgy. Know what I mean?

Anyway, I know what to get you for your birthday now.

If I knew when your birthday was.

And if I liked you enough to get you a present.

--
AndrewR, D.Bot (Celeritas)
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BOTAFOT#2,ITJWTFO#6,UKRMRM#1/13a,MCT#1,DFV#2,SKoGA#0 (and KotL)
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The speccy Geordie twat.