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After going through multiple cycles of ...
PB blaster, purple power, evaporust, shaking with 10mm bolts, oxiclean, etc. I've reached the point where most of the original rust&gunk is gone, but the tank isn't 100% clean. I also can't image the remaining black gunk is going to come out just by sitting in gas and plan to put an extra fuel filter in line that can be easily removed, cleaned, and re-installed.

So ... given the images below, if it were your project what would you do ... install and ride or try yet another cycle, maybe using vinegar this round? Obviously a perfectly clean tank is always preferred, but has it reached the "good enough" stage, in your opinion.

The reddish fluid shown is MMO.

View looking through the opening for the fuel gauge sender unit View looking through the regular filler opening

That isn't clean enough for me. It has to be perfectly clean steel before I finish. Here is what I do:
1. Use acetone and and muriatic acid to get dried gasoline and rust out.
2. Flush it with water. You will see surface rust quickly.
3. Use Krud Kutter Rustex to remove the flash rust and this prevents further rusting.
4. Then I use Acetone to remove any residue. Just a few minutes of shaking and then use an air hose to completely dry it out.

The best product I have found to prevent the flash rust is Krud Kutter Rustex rust remover. After you have the tank rust free, add a quart and shake it for five minutes or until it is completely clean and then drain it. You can just let it dry and it will prevent further rusting. You can also just use acetone after you drain the Rustex and dry it out quickly.

I agree that tank is still sketchy at best. I would try Muriatic Acid to attack that crud. I am not sure if full strength is too much, yet you could try a small amount at full strength to see what it does to the crud when it is placed in there. The Evaporust does leave behind a film that prevents flash rust, so you already have that to use after the acid dip. Use baking soda and water to flush and neutralize the acid afterwards then the Evaporust. It does need to show at least some clean metal, yet what is still down there is hard to determine.
Murphy's Laws says that is a perfect scenario for carb problems down the road if left as it is now.

Two questions on acid baths ...
1.) does the tank have to be free of all all the MMO residue via detergents or will the acid work thru the MMO? Evaporust likes it to be oil free, but I don't know if acid wants similar pre-treatment.
2.) do I have to fill the tank with acid or can I use 1-2 gallons and reposition the tank to cover all the walls?

thanks

1. The acid won't remove the dried gasoline and probably won't be too effective on the MMO. Use acetone to get the dried gasoline out. Buy a gallon and you will probably only use a quart of it.
2. Buy a gallon of muriatic acid and you will probably only use about half of it. Try about a quart first. Be very careful with this stuff. Use safety equipment including a face shield and don't breath the fumes as you gently shake the tank. I let the wind carry the fumes away from me.
3. Go back to the acetone and you will probably get more dried gasoline out.
4. Try some more acid and you will see it will be pretty clean inside. I think you have mostly dried gasoline in your tank but it is hard to tell for sure. The procedure I use typically takes me less than 30 minutes to have a clean tank.

Whatever you have been using is ineffective so far and yes be very careful with the acid as suggested with the fumes and splashing around, so wear PPE. Without knowing what’s on the tank bottom it is hard to give solid advice. The flush of the MMO and other chemicals is a good idea though.
My experience with Muriatic is limited, yet it was quite aggressive on rusty bolts that I replated with a zinc solution and quickly removed the rust. If your diluting it always add the acid to water, never water to the acid. As I suggested a small test area first, I don’t think you need more than a few litres. Let it sit in various positions in the tank to clean up each section and I wouldn’t shake it up. It will attack the rust quickly and aggressively.

flyin900 wrote: ↑Fri Mar 05, 2021 4:02 am Whatever you have been using is ineffective so far

Hah, you should have seen the "before" pictures, they were much worse than what I posted at the start of this thread. The process mentioned at the start had worked well on 90% of the tank, I'm just trying to get the finishing touches.

Here's a before pic

A cheap alternative is buying citric acid crystals. They dissolve in water (distilled is best) and work pretty much like evaporust. You can find it on Amazon or a local wine/home brewery store. I think I used 2 kg of crystals to five gallons water. Like Evaporust, it is reusable. It is also safe to touch and environmentally friendly for disposal.

The other crazy poor man’s tank cleaner is your clothes dryer. Place a liberal amount of bbs, nuts, washers, or whatever in the tank, tape or seal the openings, place the tank in a large blanket and put it in the dryer to tumble without heat. If the blanket takes up all the space, the tank just rolls around . I used cotton rope to tie up around the blanket so the tank couldn’t work through. Get it all ready and send the wife shopping for few hours. (I removed the fuel level sensor.)

I used the acid mix for two days, tumbled, rinsed and repeated for two days,

I also recommend using a mirror to see the top section of the tank where more condensation likely occurs and hence more rust.

Ewwwww, that’s ugly ! I wouldn’t use it, that’s a mess in the making. Me ? I’d get a couple of bottles of toilet bowl cleaner, put them in, close it up and shake it a bit, then open it up and fill with water (still with the TB cleaner in it) and let it sit a couple of days. Open it up and drain it out into a bucket and see if it’s clean, really shiny metal clean, not what you have above ! If it’s clean then flush it good with water, check for pin-holes and go from there. If it’s clean either store the TB cleaner for future use or use it to clean the toilets.

If you decide to seal it make sure you remove the screens and plug the lines.

I recently read about but have not yet tried LimeAway. Its a household faucet cleaner and I watched a guy on youtube make rusted chrome look like new. So it does remove rust and quite easily. My tank has rust in it, too. I just found some rust in my fuel filter Sunday (March 7, 2021) and my low speed throttle has some surge in it, so I figure its rust particles in my jets. I have to pull my tank and clean it, so after a lot of prayer and sacrificing my one chicken, I am thinking of pouring a bottle of limeaway in my tank and sloshing it around for a few days, then opening the fuel cutoff to the reserve side and draining the lime away through there to clean any rust that might be in it. My ride is a '78 GL1000. It won't hurt the metal and it did do an eye-popping job on the chrome's rust.

When I get the rust out I will seal the tank with something. Don't know what yet. And I might not use limeaway. Maybe first I will take an untreated piece of steel that is rusted up and soak it in a small bowl of limeaway to see how long to soak it and how good it works. Or I might buy a clean tank off ebay.

sounds like you are considering options

I lived with a rusty tank for a year or so. Two inline filters etc. Rust still got in the carbs, my carb guy called it shadow rust, it will still form into chunks. I did muriatic acid and a liner. I plugged the holes with rubber and worked in a large plastic tote. Good luck with whatever you try next. I'm not convinced mine is permanent, a 750 tank I did is rusting already.

I have used Red-Kote and Caswell with good results. If you want to do the job with confidence, seal it. I still get the tank very clean even if I seal it.

UPDATE - It's getting better, but still not up to the standards mentioned in this thread. The rust seems to be gone, but there is still some surface scaling and green flakes that came out the last time i drained the Evaporust. Trying 30 Second Miracle Outdoor cleaner today (UPDATE - Did not work and might have made it worse. Not worth the time/money.) , then maybe CLR or similar.

here's the latest pic

So what did you use to get it there? Given the screens are removed I would consider lining it with Caswells or Redcote after your finished, to bond the remaining material and seal the tank interior. Use compressed air to blow the lines to clear them of the liner material when lining the tank.