Corroded fuel tank for KZ250LTD

Hello,

I am currently restoring a KZ250LTD fuel tank, however i took it to a motorcycle shop and they said that it would not be worth restoring it and that i'd be better off buying a used one.
however i'd still like your guys' opinion on it and maybe some help with finding a replacement. 

Kind regards,
Tijn ''Aviator''

Is that bubbling paint on the top surface due to rusty metal?  If so, the shop may be right!

What you can try, is first remove all the paint.  Paint stripper or sand off the paint.  Then, get a large plastic tub, large enough to submerge the tank in derusting sauce.  I like a mild phosphoric acid solution, but you can use vinegar as well, it just takes longer.  

While derusting, if holes form through the metal, that's your clue that the tank may be beyond help.  Small holes can be fixed, but larger leaks suggest the tank is scrap metal.

To fix pin holes, you can braze them, or use a thick fuel tank sealer product.  You have lots of different options...

that bubbling is indeed due to rusty metal, i don't know how deep it goes on the top and whether there is rust on the top on the inside as well.
how would i go about making this mild phosphoric acid solution?

if all fails i will have to look for a new one, but it's not easy to find fuel tanks for the 250. so any advice on that would be much appreciated.

Check hardware stores in your area for steel etching solution, concrete etching wash, paint preparation materials, etc.  Do some work searching.  Check the SDS and look for something with phosphoric acid solution.  Oxalic acid will work also, as well vinegar.  Don't use HCl/muriatic acid, that stuff is way too harsh.  

From an old old old topic, jeff.saunders (Z1Enterprises) recommended using a marine epoxy coating from West Marine for fuel tanks that are pretty far gone. see link below.  For any coating preparation is key. I don't know how far you can go with a very rusty fuel tank.  Also, I don't know if anyone does this any more, but radiator shops are one place to have a tank stripped. not sure if this is a good idea on a badly corroded tank.

www.kzrider.com/forum/6-paint-a-bodywork...-badge-options#33824

I guess from a safety point of view given that you have 3 gallons of gas between your legs, if the structure is too fragile to stand stripping it's probably unsafe. Imagine dropping the bike putting it on the stand with a hot engine which could rupture a weak tank and send the bike up in flames!

It looks like something from above caused the paint to blister. Note the area that was under the seat is ok. Sides and bottom look good too. A tank usually rusts from the inside out and at the bottom. Before taking the tank down to bare metal, pressurize it to 10psi and see if there are any leaks. Also, find out what caused that damage. I want some for stripping my next tank..

i myself had concerns about the structural stability, i have decided not to attempt restoration of the part as i'd rather have a tank i can rely on to be safe, which to me as an aviation technican is quite important.
however this leaves me with a problem, i need to find a fuel tank thats in a good condition in the netherlands. this has proven difficult as the KZ250LTD was never sold in the netherlands.

the story of this bike that this bike was sold in germany, drove 8000 kilometers, stored for 30 years, bought by a belgian, and then bought by me.

I also do not know what caused the paint to blister, i'd assume the top of the fuel tank was exposed to the elements. but that doesn't make sense to me as the rest of the bike is in a good (although dirty) condition, so your guess is as good as mine. it has a german VIN number which i want to decode somewhere to see what has happened to it in the past.

if there is any more information you'd like, feel free to ask

I restored a rare tank one time that had a ton of rust.  During the derusting process, it sprung a leak, which I soldered closed.  Back to derusting, and again, same thing.  After about the sixth leak, I put the tank in a tub and submerged it in the cleaning solution (phosphoric acid).  Once the tank was derusted, there were several small holes, which this time I taped over (no more brazing).  To seal the tank, I used Caswell Plating Epoxy tank sealer.  That stuff is THICK.  Like cold honey.  I used the entire quart, and moved it around inside the tank, coating the inside again and again, until the epoxy kicked off and firmed up.  That tank never leaked again.  It was also several lbs heavier than it was before, because of the sealer.  

No eBay APP ID and/or Cert ID defined in Kunena configurationThere are some listings for tanks on Ebay (in the US) Kawasaki part# 51001-1039 there is a letter/number after it that indicates color. Not sure if you can see US ebay in your location?

www.ebay.com/p/1476241448

Having said that I would put it under pressure as suggested and see if it leaks, if not I would strip the paint and then de-rust inside either with chemicals or via electrolysis.

Absolutely agree that if the tank is structurally sound then soldering, brazing or "lead loading" any pin holes to seal would be fine (in combination with a liner) my safety comment related to if the corrosion was bad enough for stripping to be a concern due to "structural instability" worst case would be that a chemical strip leaves holes big enough to put your finger in. The 250 tanks are rare outside the USA with shipping as much a the part but might something else for a more common model like the 305 be adapted to fit? Difficult to cross reference the part number quickly on CMNSL as the part number includes the colour code (last three digits) perhaps a few hours of research might turn up an alternative
If everything else seems ok it may have been the victim of a brake fluid spill etc (some people don't realise how effective a paint stripper brake fluid is when it gets somewhere you don't want it)

The more I look at the paint on the top of the tank and the shape it is in, I think it may of sat below birds. Like in a chicken coop or shed that birds were using overhead rafters etc and sat in bird poop for way too long. Truth be told it does not take too long to create issues with paint. I know I have seen things on line that indicate bird poop will mess up auto paint rather quickly unless it is cleaned up.   Bird deposits contain a high amount of uric acid with a pH level somewhere between 3 and 4.5, which is quite acidic.  Uric acid is corrosive, and it quickly eats any wax or sealant and cuts through the paint. If that is what has happened then the metal of the tank my be OK but you will not know until the paint that is still there is removed.