gas tank is full of sludge.

Yesterday i bought a 1979 KZ650 and a truck full of parts. i am new to the forum and the bike. the bike does not run and was sitting in a barn for the last 10 years. my first course of action is going to be cleaning the gas tank out. the inside of the tank is rusted and full of sludge. Can anyone tell me good methods or products to buy to clean the tank properly? thanks.

Por-15 sells a gas tank restoration kit that includes three products: varnish cleaner, derusting phosphate sauce, and a sealer paint. Good stuff that truly works. Key thing is to make some good plugs for your tank, don't use the petcock for example, and allow the phosphate to remove all the rust (may take a day or more). The info on the Por-15 website suggests that you don't need to remove all the rust but don't believe them. Fully derust and then seal. I've done several tanks so send me a PM if you have any specific questions about the process.

Good luck

One of the most common tasks associated with bringing an older bike back from the dead is figuring out how to deal with the varnish and rust, in the tank, left over from years of neglect. After cleaning many gas tanks, I've finally settled on this method as working best for me. I'm sure there will be refinements and improvements, of which I'll write more about as they evolve.

First of all.
Why do fuel tanks attract moisture?

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.

What to do if you find rust in your tank.

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.

Bill

$15.78 will buy you a gallon of Etch and Prep from Home Depot (phosphoric acid)... www.homedepot.com/s/etch%2520and%2520prep?NCNI-5

Same basic stuff as sold by Por-15 as "Metal Prep", and included in the gas tank restoration kit.

Same basic stuff as sold by each and every automotive paint manufacturer to prepare bare steel for painting.

Same basic stuff as used by powder coaters to prepare the metal to be coated. Sorry to belabor this detail but hope you get the point.

Phosphoric acid does not need to be neutralized other than by rinsing with clean water, something that can not be said of muriatic acid, which in comparison is significantly more dangerous. Honestly, I'm not some chemical ninny and can respect the process that Bill has laid out here for the muriatic acid, but I honestly don't see the point of using that stuff when the proper material is cheap, easy to work with, and safer.

Nessism wrote: ... Honestly, I'm not some chemical ninny and can respect the process that Bill has laid out here for the muriatic acid, but I honestly don't see the point of using that stuff when the proper material is cheap, easy to work with, and safer.

Because phosphoric acid will not clean away thick or scaly rust like muratic acid will. I've tried just using phosphoric acid. It just doesn't get the job done.

Bill

Congrats on the find. Have fun with it

My method is pretty simple.
Check for weak spots and sound the tank(gently thump around the tank with a socket extension) looking for filler. If you hit filler the sound will go from a tink to more of a thud.
If you find filler,remove it with 80g on a DA or random orbital as there may be epoxy filling a hole.
Once you know the tank is sound,
Remove the petcock and make a plug to bolt on with a paint stick or other thin wood and bolt it in place of the petcock with a piece of a rubber glove sandwiched between the "plug" and tank.
Remove the gas cap and use the rest of the paint stick to drape out as much of the varnish as possible. Pour in a half a gallon or so of fresh gas and a handful of bearings or small nuts but be sure to count them to make sure all are removed in the end. Agitate.
His will remove the majority of the remaining gunk.
Next I use a strong degreaser like LAs totally awesome degreaser and pour a quart or so in the tank and give it a swish for a few minutes. Dump,rinse,dry.
If scaled rust is present I'll use a sealer such as kreem or pour.
If no scaled rust is present then pour in a pint of ospho. Shake well,dump,dry.
Go back with the bearings or nuts and shake them around the inside to knock off any of the heavier oxcide deposits,dump the nuts,blow out with compressed air and the tank is ready to go back on.

I'm sure some will argue with my method but its cheap (around $20) and it has worked very well for me.

Cheers,

Always used distilled white vinegar and steel BB's. In a clothes dryer packed in with towels on no heat. Tumble adjust position and re-tumble. Rinse -repeat of necessary. Never worried too much about flash rust just don't want particulates or scale. Always use in-line filter too.

Steel BB's so you can fish the hard ones out with a magnet.

thanks for the suggestions. the gas tank does not leak and the metal is not weak. Ill probably use bb's or shot mixed with a solution to clear the tank. i do also want to get a tank sealer after the tank is clean.