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Hi Folks,

Seems as if all of us struggle with this one, usually more than once. Here's a write up I did some time back. It's still the method I prefer but that doesn't mean it's the only or best method so please feel free to post your techniques and tricks as well.


You park the bike with a quarter tank of fuel probably during the day when it's warmer. That night the temperature drops and as the air inside the tank cools it becomes less able to hold moisture so some of the water vapor condenses. Now this amount of water is insignificant and over night or even a couple of weeks won't usually be a problem. But over a longer period of time, usually months, the tank will breath in every time it cools. That new moisture will condense then when the day warms up the tank will breath out the air that gave up some of it's moisture yesterday. That night as things cool down the tank will take a new breath of damp air and the process starts over again.




Is the tank leaking? If it is either Pour 15 or Kreem will solve the problem. Pick one and follow the prep instructions carefully.
If the tank is still holding fuel, I like to check the quality of the steel at critical locations before I go further. To do so, I use a popsickle stick and test the areas adjacent to the seams. Set the tank down and run the popsickle stick along the seams using moderate pressure. Find the lowest part of the tank and test this area as well. If the popsickle stick can't push a hole through the steel there's no need for epoxy sealers. Great, you're bucks ahead and your bike will be worth more as well. As a collector, I've learned to always check the gas tank, not only for rust but to see if the previous owner has had the tank sealed. I judge a sealed tank as hurting the value of a bike more than a rusty tank.

If the popsickle stick reveals soft areas but doesn't actually puncture a hole, It's still a good idea to go with a sealer as the cleaning process may well cause the tank to leak after all.
There are plenty of methods used to clean gas tanks.
I've used sand with steel nuts and kerosene and tumbled them for hours. I gave up on abrasive methods because they take too much time and the sand is too difficult to clean out when finished.

I've used mild acid preparations such as Naval Jelly. These I gave up on because they don't really attack the rust enough to get rid of heavy build ups of scaly rust.
I tried the electric method, using a battery charger and a steel rod. I'm not sure this one accomplishes much. It didn't touch the scale and getting at the top of the tank is tough.

I've read about using sodium hydroxide ( lye ). It's supposed to be a good method because it doesn't erode the base metal. I'm looking forward to an opportunity to try it out.

Most recently, I've settled on a muratic acid wash followed by a dose of phosphoric acid as the best method, mostly because it always gets the job done and doesn't require a lot of physical effort.

To do the job you first have to decide if the tank has scaly rust or just surface rust. If the rust hasn't gotten to the point where it's scaly you can skip the 1/4" nuts, referred to later.

First, flush out any oily varnish that may be coating the lower regions of the tank with acetone or any of those engine degreasers. If you choose the engine degreaser flush the tank with water.

Remove the fuel level sensor. Seal it's opening with GOOD duct tape.
Remove the petcock and seal it up with an appropriate plug or capped section of hose. Dump 30 or so 1/4" nuts into the tank.
Pour in a pint or so of muriatic acid. Seal up the fill spout with GOOD duct tape.
While wearing gloves, old clothes and safety goggles. Agitate the tank for 10 to fifteen minutes. During this time you can monitor the pressure in the tank by watching the duct tape bulging at the fill hole. If too much pressure develops, carefully vent it by peeling the tape back than reseal and keep shaking.

Next pick a piece of concrete that you don't particularly care about. Remove the tape from the sender opening and fill hole and flush the tank with cold water. The acid that has not already been consumed will neutralize itself on the concrete. You're still wearing goggles and gloves right?

Now dry off the openings and reseal them with GOOD duct tape. This time pour in a pint of naval jelly, or milk stone remover or tile haze remover. These are all phosphoric acid formulations. Phosphoric acid is not as aggressive as muriatic acid and therefore is mostly a waste of time if you're trying to really remove rust. What phosphoric acid will really do well is leave the inside of the tank coated with iron phosphate, which is somewhat rust resistant. For this step you do not need much agitation. Just tumble the tank over several times and let it set for a half hour or so and then tumble it again. After about two hours of this and go back to the concrete slab, open the tank, drain it and immediately spray WD 40 into the openings trying to coat as much of the metal as you can. Now flush it out thoroughly with clean water. One more application of WD40 and you're ready to force dry the tank.

Back in the shop, prop a blowdryer so that it forces warm air into the tank and let it blow for an hour or more. Position the tank in different orientations during this process to make sure that no seam holds water. Once it's really dry you're done.

I used to say that the phosphoric acid step was critical to avoid flash rusting. Now, I still think it's a good idea for future rust resistance but since I started spraying WD40 into the still wet tanks, flash rust's no longer a concern.

I've probably cleaned twenty tanks with some variation of this method I've described here and never damaged the exterior paint or eaten through the steel.

Good luck.

Thanks for the interest.

Bill

Thanks for making this a seperate thread Bill! Makes it easier for people to find .

I've done good deal of research into this topic as well so I'd like to share my two cents . When I bought my first KZ1300 last year, the rust was so bad I was genuinely concerned that I would need a new tank and that cleaning it would be beyond me. Plus I couldn't let it sit because rust chunks were getting everywhere throughout my fuel system and causing all sorts of havoc. It had clogged the petcock, in-line strainer, and carbs so bad it made the bike unreliable to drive.

I'm not the type to give up easily, though, so I set out to research the best method for my particular lifestyle and budget. What worked best for me was Evaporust. It works by absorbing the rust into the liquid leaving all the clean metal behind and is completely non-corrosive. I was able to fill my tank most of the way with it and every few days just turn the tank over. Within a few weeks the rust and all traces of it (except for the pitting from the lost metal) were gone and the tank looked new. I was amazed with how well it worked plus I didn't have to put any abrasives in the tank.

After the tank was clean I was able to drain the evaporust into a container and continue using it to de-rust all kinds of other stuff like my exhaust system, motor parts, bolts and whatever I could fit into the container lol.

May not be ideal cost-wise for everyone since that stuff is like 20 bucks a gallon and you'll need like 3-4 gallons of it. This seemed like the safest method for me since I was forced to leave the solution in the tank for weeks on end due to my busy lifestyle (full time job, wife, toddler children and a multitude of other projects).

OK here is your worse case rusted fuel tank it is on my 79 KZ 1300. In the 17 years my tank set on the shelf a mouse found its way into the inside of the tank. Last year when I started mt rebuild project it didn't not include replacing the tank. And as we know finding these tanks in good shape is every hard. So here was my fix. As you can see in some of these pictures there was quite a bit of holes in the tank big and little thru out the tank. The cost of this fiber glass job was about 150.00 buck U.S. money and then two bottles of sealer to coat the inside of tank after I was done was $50.00. Now you have to realize this is a work of love. I guess I am one of of few that likes the looks of the 1300 tank so I set out to save it. You have to put a heat shield on the bottom of the tank after you do this so the heat won't soften the fiber glass in the tank. It does work I will post a picture of the finished tank. I still have out side finishing work to do to smooth it all out and the paint but llike I said its a work of love.

Wow wrgoo56 that tank was pretty far gone . Most impressive work!

Were you able to get the tank painted and back together without any evidence of the rebuild showing on the surface?

Its still a work in progress. I have the left side smooth out now and part of the top still have the right side to do but it been on the bike and I been riding for the last 4 months. I will post some of the later pics as I go.

WRgoo56.

Lovely job that mate, a real result.

You must have lots of patience & skill !

Pete F