Came out this AM and opened the garage door to the overwhelming smell of petrol. A quick check showed nothing around the lines/injectors/throttle bodies ... but a closer inspection along the bottom edge of the tank (partially obscured by the fairing) revealed this:



I don't know if you can make it out, but it looks like the P.O. put some kind of putty or adhesive over the spot to hide the leak when I picked it up. Unfortunately, if he blows off my email and calls to "make it right" I am stuck, as this was an "as is, where is" sale and there is no lemon law on private transactions.

Anybody got an idea how much a tank repair would be? Or if not, what do you think a used tank should run for an '85?

Thanks forum brothers and sisters!

Paddy

Don't be too despondent K100Sprint, leaks, particularly around the lowest section where the fuel pump sits, are quite common.

Both my K's have been fixed with 'JB weld', and it's held for more than 15 years in both cases. There are many 'fixes' on here so try the search facility. I seem to recall some members having success with Permatex products.

Good luck,
Paul.

Try POR15 fuel tank repair

Very common. Had it on both my K's.
Epoxy putty is a pretty good fix. Especially if you can hide it in behind the fairing and that's usually where they go. As Paul says, near the fuel pump. Use new putty each time. It goes off after a while.
Although my '84 developed pin holes in the base.
They usually blister first. My '89 went into a 3mm hole when I poked the blister.
I would try to repair the original tank. Even much younger tanks could be the same.

From what I can understand, over the years you always get a tiny little bit of water mixed with the gas or entering the gas tank when it's raining and you open the gas cap.
Water being heavier than gas, it seats a the lowest point of the tank and slowly corrodes the aluminum.
As a preventative maintenance, every 2 years, I empty my tanks and clean them.
The seam where K100spring has a leak is very common.
My advise is when you repair the leak, spread whatever repair product you use way over the pin hole.

Quick temporary fix:
Take a bar of soap and shave little pieces out of it. take a piece of bread,  a bit of water and start to mix the bread and soap to get a sticky paste. Stick it on the leak and voila....
I spent 6 months in Africa with a big gash in my jeep's gas tank that was 'repaired' with this solution.
IT WORKS!!

CF

No sweat. Permatex make a kit that you can use without having to dry out your tank. I've used it (twice as I was stingy with the patch first up) So far, 2 years with no problems. My patch was black stuff, doesn't look so good if I ever upended my bike.

Did anyone ever hear of or try a repair with this stuff.  In the video they repair a hole in a soda can.  Downside is that you will need to do a paint job when you're done.  Interesting stuff.

http://durafix.com/index.html

I'd deff. try any repair from the out side (patch) first before you resort to any method of lining from the inside, like the POR15 robmack mentioned. If the lining method dosn't work its a real bugger to remove for a second go, unlike the patch from the outside (permatex)

I had the same issue, pinholes in the corner of the tank.  I widened them up a tiny bit, got rid of any soft edges, Used JB weld and then did Red Kote inside.  Still putting the bike back together and hoping it holds.