Just had the same problem. The tank is from a CBX1000 that was lined when it was painted maybe 10 years back. I don’t know what the liner was, but it started to lift a couple of years back. Everyone wants to blame the ethanol we have in fuel these days, and maybe that is the reason, though I do wonder if inadequate preparation could well be the problem.
I bought a UK product called “sealeater” which allegedly removes all tank liners….
https://www.ebay.co.uk/itm/Fertan-Fuel-Tank-Sealant-Epoxy-Resin-Remover-1-Litre-SEALEATER/262495192437?epid=13008016677&hash=item3d1deec575:g:7mMAAOSwbYZXa-4oIn my case I wanted not to have to re-paint (and of course anything capable of removing epoxy tank liners will kill paintwork – even the vapour will damage paint). Half a day masking the tank using adhesive backed silver foil (similar to that used to seal double glazed window units here) and thick plastic sheet did the trick. I did use maybe 4 layers of plastic and probably 10 layers of adhesive foil around the filler neck and petcock spigot. So the sealeater was poured in and left for 24 hours, with the tank moved every hour or so to allow the liquid to cover the various areas on the inside of the tank. The cap was fitted and the petcock spigot plugged so that the vapour was contained within the tank.
When the tank was emptied, quite a lot of the old sealant came out in smallish pieces, but not all – especially on the center “hump” within the tank. The problem appears to be that you cannot immerse all of inside surfaces of the tank when you are using only 1 litre of sealeater (CBX tank is approx.. 20 litres capacity.
Maybe I needed to leave the sealeater in for longer, maybe I needed to buy several lots of sealeater.
I’m my case, my attempts to remove all of the old liner have not been successful so far, though the paint on the tank has survived undamaged. From what I can see, about 75% of the old liner is gone.
I will use a tank de-rusting solution next to remove surface rust from the mostly now visible metal areas inside the tank, sutface rust being the reason for the fitment of the liner previously.
I will probably re-fit the tank for next season and see if anymore sealant breaks free – previously the old liner came away in largish pieces, and the CBX does have a fine mesh filter inside the tank.
Not sure the above helps you Steve, just my experiences so far….
Chris R.