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How to immaculately clean a gas tank?

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ctfarmer
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2025/05/04 18:09:29 (permalink)
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How to immaculately clean a gas tank?

I'm attempting to resurrect a 1980s Honda FR500 rototiller with a Honda G200 engine. 
 
I've managed to get it running (poorly), but I'm currently stuck on a problem the internet hasn't been able to solve for me. 
 
While I'm able to get the engine started, the carburetor clogs fairly quickly. When I've opened the carburetor I've found gritty, sand-like particles inside. 
 
These particles are almost certainly residue from the gas tank (which had been full of stale gas for about 20 years). 
 
I tried to clean the gas tank by filling it with some pennies, and fresh gas, and shaking it all around. But that didn't do much. I doubt filling it with gravel and shaking it would clean it very well either. The residue is on there pretty good and it covers maybe 25% of the tank's surface. The gunk is a dark brown/green color and has a slimy appearance, with tendrils. 
 
I've tried acetone, too, but that didn't get all the gunk off. 
 
So my question is: Is there any foolproof way to 100%, immaculately clean the inside of a gas tank besides gravel, nuts and bolts, acetone or vinegar?
 
Thanks for any thoughts you might have. 
 
P.S. I'd like to simply avoid the issue by installing an in-line fuel filter, but the gap between the tank and the carburetor on the G200 engine is so small I'm not sure that's feasible. I'd have to use do a loop-the-loop on of the fuel line to make the filter fit, and I'm assuming that would cause problems? 
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    Conrad Sigona
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    Re: How to immaculately clean a gas tank? 2025/05/04 18:59:36 (permalink)
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    I had a similar problem 40 years ago with a gas tank for my car. I solved it not by cleaning it immaculately, but by cleaning it adequately (using pebbles, chains, soap, brake cleaner) and then lining it with a plastic coating. No matter how much I had cleaned it, there would still be a residue which wouldn't take long to clog up the fuel filter. At the point of giving up and ready to buy another tank, I found out about this stuff that you just pore in, swish around, pour out, and let dry. Each cycle of pore-swish-empty-dry leaves a thin lining and you repeat it as many times are you need to. At the end, to prove to yourself that it works, you can pore in some fuel, swish it around, and dump it out through a coffee filter. If anything discolors the filter, you have more work to do.
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    SRTsFZ6
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    Re: How to immaculately clean a gas tank? 2025/05/04 21:10:53 (permalink)
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    Muriatic acid will rid the rust.  
     
    100% it's EXYTREMLY STRONG, and dangerous if you breath it in.
     
    You can dilute it with water, 4:1, 5:1 monitoring it closely. It will take off paint too.
     
    POR Tank sealer (and other products) work VERY WELL on metal fuel tanks.
    They have tank cleaners as well that work very well...
     
    .

    Scott
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