I acquired this 96 K1100RS a little over a month ago and it sat in the garage for about 3 weeks with 1/4 tank of gas with no leaking. About a week ago I filled it to about 7/8 full. It is now leaking fuel from somewhere under the gas tank. There is gas on the top of the black plastic box just under the rear of the tank. (see pic).
Does anyone have an idea on what is likely to cause this leak?
Thanks,
Craig

Check out for bubbles in the paint work they are a give away for a small area of corrosion or the big O-ringwhich is under the plate that holds the wiring as it enters the tank. The insulation under the tank may be soaked with fuel and need to be dried.

Thanks Rick,
It was the the big 0-ring. All is good now.

Maybe mine isn't as simple as a leaky "O"-Ring!

Having stripped off the "temporary" patch applied by a previous owner I now understand why it was struggling to contain the leak, and which took it off the road 8 years ago!




DSC_0016 by Ian Johnson, on Flickr" />

[img]DSC_0018 by Ian Johnson, on Flickr[/img]

That is about the biggest corrosion hole I have seen in a K tank. Congratulations Ian you appear to be the winner.  
It is a bit beyond a simple patch and should be fixed by cutting the corroded area out and welding a new piece in and not over the hole as that will promote more corrosion.

Reports such as these are a puzzle to me.  The interior of my 1985 vintage tank appears absolutely new.  There is no hint of corrosion anywhere inside, and it isn't lined with anything that I can detect.  After so many years in service, it's odd it appears new. Why do some tanks fail?  Is that inevitable?  I know aluminum is subject to oxidization when left to the elements (I'm thinking of a radio mast now), but I thought keeping aluminum covered with fuel would prevent corrosion.  Question: is it better to have the tank topped off with fuel or empty in storage?

I empty mine and remove any filler caps and petrol (gas) taps. Steel tanks then get a slosh round with engine oil to coat the insides and get stored up in the roof of the garage over the oil burner where it's (usually) warm and dry.

i've got a k75s tank with two holes in the bottom left side at the lowest point where water-fuel (10% ethanol) will collect when the tank is on the side stand.  The tank had been painted with a thick coat of a heavy flex agent paint. 

There was a slight drop of fuel sitting on this strange bubble under the tank edge--which promptly emptied the tank when i probed the bubble to see what it was.  The water had eroded a perfect circle in the tank about the size of a pencil, and the paint was the only thing holding the fuel in.  Just lucky it didn't open up on the road.  Now i go out of my way (and pay more)  to find and only buy pure gas.

i doubt they are using 200 proof alcohol to add to the gas so there is already a water content to begin with, but alcohol absorbs water from the warm moist air and the water collects in the bottom of fuel tanks and does it's destruction.

kennybob wrote:i doubt they are using 200 proof alcohol to add to the gas so there is already a water content to begin with, but alcohol absorbs water from the warm moist air and the water collects in the bottom of fuel tanks and does it's destruction.

While the gummint is trying to make us use 10% ethanol fuel in NSW (to support their ethanol producing $$ donors), we at least have some ethanol free fuel.
I won't use ethanol fuel even in a lawnmower, let alone my boat or bikes! 

Bill

Any water in the fuel tank will be absorbed by the alcohol and will pass harmlessly through the system, it is when water is left to sit in the lowest part of the tank that the electrolitic action takes place and makes holes in the aluminium.
If I ever get into the situation of having to use low octane fuel like 91 (and I have had to do it a few times) in Australia or 85 in USA then I use fuel with ethanol because 91 alone will cause detonation which is harmful to the Nicasil bore where 91 with ethanol will cause much less detonation, I just make sure to run a couple of full tanks of 98 afterwards to remove the ethanol which will cause long term damage to the rubber components.

There have been many posts on this difference over the years and AFAIK 91 in Australia is the same fuel as 85 in USA and probably all of NA.
Alcohol will not detonate anywhere near as much as Petrol (gas) so even 10% ethanol will prevent the detonation that low octane fuel causes.