Removing thick varnish from small steel fuel tank?

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409
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Tacoma, WA, USA
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I have an old rare model Honda Gyro scooter I am semi-restoring (replacing the trashed engine and other bad parts) and the fuel tank has a MASSIVE amount of thick, black varnish in the bottom. When shaking it out, it looked like clumps of mud. (And it could be mud, given the transmission had mud in it.. but it's varnished too) I removed as much of that as I could, then took the garden hose to it until water was coming out fairly clean. It only has one accessible hole down into the tank, and that's the couple inch wide filler hole, so I can't reach my hand down in to clean it out. When I scraped the bottom with a flat head screwdriver, thick black crap came off (like what was shaken out) and I could see the shiny metal of the bottom of the tank, so it's not rusted out in the bottom. What's the mildest liquid solution that might help dissolve the varnish without being able to reach in and scrub it? If it has to sit for a week, that's fine. Some people like to use metal nuts to bang around, but I'd be concerned about sparks. Some people say to use gravel, but that can shed particles. Glass marbles or instead maybe?
 
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929
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New York
I'd go with lacquer paint thinner or acetone. Same effect but cheaper. Stuff sone chain in there and shake it around every time you wander by. If it's still rusty after you're done decruding it you may have to Kreem ( I think that's how it's spelled) it.
 
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409
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Tacoma, WA, USA
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Originally Posted by Cujet
Berryman's B12 liquid. It will dissolve most varnish. Get the can with the screw on top.
Thanks for the suggestion. This looks to be it.... B12 15oz O'Reilly auto I have a couple O'Reilly gift cards from 15w40 oil rebates I got earlier this year, so I can get a couple of cans for "free". Maybe one will be enough, especially if I mix some fresh gasoline with it to help fill the tank up better. I'm guessing the gasoline would be ruined though when mixed with the varnish? It's very hard to properly get rid of anything except engine oil around here.
 
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409
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Tacoma, WA, USA
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Originally Posted by Driz
I'd go with lacquer paint thinner or acetone. Same effect but cheaper. Stuff sone chain in there and shake it around every time you wander by. If it's still rusty after you're done decruding it you may have to Kreem ( I think that's how it's spelled) it.
Yeah, I was considering acetone or something like that. A gallon of this is $15: https://www.walmart.com/ip/Klean-Strip-Lacquer-Thinner-1-Gallon/35656764
 
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1,906
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Seattle-ish, WA
Quote
Berryman's B12 liquid
This stuff is great, and it's usually like $3/can at Walmart. I use it instead of Seafoam for most things in slightly lesser concentration (it's more aggressive). Check the tank well for pitting. If you see any, you need to seal (line) the interior or risk rust-through. There are a number of products for that; I have restored a few motorcycles and used Kreem with great success. There are others.
 
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Pittsburgh,PA U.S.A.
If the other methods already mentioned do not work, metal machinist use a blue lacquer paint on parts and usually scratch away where they want to make a fine line for some kind of reference. When they are done making the part they have to remove the blue lacquer. Machine shop suppliers sell a lacquer remover that is very strong that is used for doing this. The down side is that it probably is stuff you do not want to get in contact with your skin because if it gets into your body it can't be good for you. Also, when I use it I make sure there is plenty of ventilation. My neighbor built a nice brick wall with a marble top, and some kids sprayed some paint on its top. I lent him that solvent and it took the paint right off. Check companies that sell end-mills and other machining supplies to find someone who sells it.
 
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Cincinnati, USA
If it won't dissolve in gas, then it isn't a problem if some remains, therefore, gas, and some pebbles instead of nuts, or sand if it had rust. However, you'd be hard pressed to create a problem from sparks with nuts banging around if it's full of gas. It's the gas vapor that's highly combustible, and needs a sufficient amount of air to supply oxygen. Liquid gas in volume, you can literally throw a lit match at it and it will just put the match out if there's no gas vapor/oxygen mix present.
 
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409
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Tacoma, WA, USA
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Originally Posted by Dave9
If it won't dissolve in gas, then it isn't a problem if some remains, therefore, gas, and some pebbles instead of nuts, or sand if it had rust. However, you'd be hard pressed to create a problem from sparks with nuts banging around if it's full of gas. It's the gas vapor that's highly combustible, and needs a sufficient amount of air to supply oxygen. Liquid gas in volume, you can literally throw a lit match at it and it will just put the match out if there's no gas vapor/oxygen mix present.
Hopefully the acetone soak will be good enough. It's just for me, so it doesn't have to be spotless. Maybe I can get my hands on a better condition fuel tank later if this one causes problems. They aren't cheap though, about $80-130 for another used 35 year old tank. I will put a clear plastic in-line fuel filter between the petcock and carb, since the stock setup fuel filtering is just a tube sticking up in the fuel tank from the petcock and a tiny screen within the petcock. And that might need replacing with one that lacks the internal screen due to being so clogged up with varnish. It's aluminum, so it can't be soaked in acetone very long. If I can figure out the tank's threads, I can order a new one for $10, or just buy a rebuilt OEM one for $40. Once its running, always adding B-12 to the gas might be a good idea to help keep the fuel system clean from the questionable fuel tank.
 
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24,603
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Upstate NY
Isopropyl alcohol will work very well and is inexpensive (well maybe not during the pandemic). Shake it around every day. I would go for a week. Then look at the tank and maybe it will need more isopropyl alcohol.
 
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9,796
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Jupiter, Florida
Originally Posted by Linctex
Berryman's B12recipe is: Lacquer thinner and acetone (maybe a tiny bit of methanol)
That is not complete. The B12 Chemtool in the bottle is 2-Propanol 2-Butoxyethanol Methyl Ethyl Ketone Methanol Acetone Toluene Furthermore, while B12 is methylene chloride free (paint stripper component) , it's components are effective paint strippers for epoxy based paints. They are equally effective in dissolving gums and carbon. Just like conventional paint stripper.
 
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409
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Tacoma, WA, USA
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Originally Posted by Linctex
Originally Posted by Cubey
I have an old rare model Honda Gyro scooter I am semi-restoring
That thing IS RARE!!! https://en.wikipedia.org/wiki/Honda_Gyro
The one I have in the wiki article is the "Road Fox", which is the Japanese name for it. In the US, it's the 85-86 "Gyro S" and is the most common Gyro model in the US. The other one sold in the US 1984 only is called the "Honda Just" in the wiki article. This is a better page about US models: http://www.motorscooterguide.net/Honda/Gyro/Gyro.html Attached pics show how I got it and the original motor. It was in "for parts only" condition really, but I bought a used replacement motor since the original was truly too far gone. It's sitting on wooden blocks with the motor off still right now since I'm having to deal with getting fuel system and other parts cleaned and replaced, as my budget allows. I already bought all but one new engine bearing before I realized it was beyond repair, and bought a replacement one that isn't rusted and eaten away. The motor in the box is the replacement.

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