[jakec]

I got a pretty rusty tank with my CL175 and use 2 gallons of white vinegar too loosen it up. Waited a while and cycled water and gas through, avoiding flash rust for the most part. I closed the tank up and left it to sit empty while I get the rest of the bike ready. Today I went to check on the tank out of curiosity and the inside was covered in a black sooty stuff. I can wipe off some soot with my finger and it comes off on me, smelling sort of like gas and rust. The odd thing is that the inside of the tank smells sweet? now. Sort of like apple juice. I put it in the closet for about 20 minutes with the cap off and when I opened the door to the closet later, I was hit with this really strong sweet odor. So I have the tank sitting in a more open area now.

I'm wondering, what is the black stuff? I'm guessing I'm going to have to start the tank cleaning process over now..

 

[jakec]

I haven't been able to find anything online about the black stuff in my tank, nor the sweet smell. I imagine that the sweetness may be a remnant from the vinegar since I believe that it was made from apples. The black stuff however seems to be in the place of rust just... black. I am going to have to redo the tank clean-out and this time I want to do it correct. When I had finished I thought that I had only minor flash rust and then sealed the tank up. Is it bad to let the tank sit empty even if there's no water/moisture to cause further rust? *(the final rinse in the tank before sitting was about 5 or so rounds of gas swished through).

When I looked down in the tank, at the bottom I could see some glistening / moist looking black stuff as well. I assumed the moisture is gas. But the black stuff down there looked pretty plentiful. A LOT of rust came out when I cleaned my tank but I suppose there could be more sediment at the bottom. Still doesn't explain why it's black and chalky instead of orange and rusty tho...

 

[spirograph]

One thought might just be adding abrasion, if it rubs off with a finger. I don't know what the chemistry would be, but the vinegar could have catalyzed the rust/bidness on the tank into that carbon-like stuff you've got, but it's just sitting on top of the bare metal. You'll see a number of recommendations on here for abrasion, but I just used about forty 1" wood screws, dumped it in there with the diluted vinegar, and gave it a good shake every 20-30 minutes to abrade the inside of the tank. Worked a peach. I've heard ball bearings are a good choice too, just make sure you count anything in or out.

 

[jakec]

Hey, thanks for the tip. I think I'll avoid using vinegar as it leads to the flash rust. Maybe I can use some cheap vodka instead (i'm serious). Shaking gas scares me and I've already got about 3 gallons that I don't know how to get rid of. I'll buy some 1" screws and get on that.

 

[spirograph]

Shaking gasoline would make me nervous too! there are some other solvents around that people have used, though I'm not personally familiar. I had good luck with a couple ounces of Marvel Mystery Oil dumped into the tank directly after flushing the vinegar. Only other thing I'd suggest is, make sure you seal your gas cap with clingwrap (at least a layer between it and the tank), as the vinegar crystallized all over my cap gasket and cracked it from dryness.

Edit: If you go the Marvel route, just slosh it around and make sure it coats everything, and repeat every few days until it's ready to be gassed back up. The oil doesn't need to be flushed before gas.

 

[Richard Strange]

Could it be mold? If it smells sweet there may be sugar in it from the apple cider vinegar.