I did a full restoration on my 1971 Yamaha AT1c 7+ years ago. It has not had a lot of miles on it since restoration. I don't ride it as much since it has had some minor issues with the carb leaking, and trying to find a suitable carb took some time. The gas tank was repaired by acid dipping and then a coating was put inside the tank. This needed to be done since it was lined before 20+ years ago. I had a leaky needle valve in the carb which is only a few months old. This usually points to sentiment in the carb bowl/gas tank. I drained all the gas out and it was nasty. Almost black. This gas is months old, but not years. 

I took some pictures inside the tank and it appears the liner might have failed, and some rust is coming back. What should I do to fix this issue? 

Pics below. 
imgur.com/a/L9soiGo

 

Yuck man I hate that happened to you. I would buy another tank but there are some professional gas tank coating places that might help you out. I had my 1930 Model A Roadster tank professionally cleaned and coated about 10 yrs ago and haven’t had any issues yet fingers crossed. 

I used Moyer Fuel Tank Renu for my DT1 MX nine years ago. It appears they are still in business. My result was extremely good, but it is not cheap and you will have to repaint your exterior. I know from experience that finding good used tanks is almost impossible these days.

Bad news just got worse. It appears my gas tank is leaking by the petcock around the mating surface. I also noticed that the paint around there is starting to come off the tank.

I'm really sick about this after spending all this money on the tank. I'm trying to keep all the parts original to the bike. outside looks great, but it is leaking. I'm assuming this means getting another donor tank and re-doing it all.

I had similar issues on an original tank that looked really nice on the outside. I used a kreem tank sealer kit on my tank with several pin holes. I used aluminum tape over the section that had pin holes. The instructions clearly said duct tape will NOT work. However, aluminum tape worked well and held up for all three steps in the process. Rust eater. Metal prep. Final sealer. I left the tape in place because it is so adhesive I was afraid it would pull the tank liner if I peeled the tape off. I have used it for a year now and no leaks so far. I have since picked up a good solid spare tank just in case the original tank fails.
youtube.com/shorts/jEPh9XazYuo?feature=share8

This tank was completely redone. Acid dip, pinholes soldered up, and liner put in. This was done about 7 years ago. The gas I took out of it was black. I'm trying to figure out what I should do next. Sounds like either way I will have to redo the gas tank. 

Is there anyway to remove this liner?