i would go 50/50 acid/water. then when the rust is gone flush it out with baking soda and water. rinse well again and line the tank with cheap two stroke oil to prevent flash rusting.
I mostly use concrete cleaner now which is phosphoric acid. It leaves a coating which doesn't rust further. Muriatic acid leaves the metal bare and it surface rusts quite quickly.
That said, if your tank isn't too bad, use 1/3 acid to 2/3 water or less. Better to have things take a little longer than go too quickly! Definitely coat the tank right away after flushing with a baking soda solution.
ok so i plugged the fuel tap hole ,i cant believe this thing ran
with that much rust ! do you think this stuff eat the rubber
on my gas cap? I saw in the lambretta manual you could put
in marbles to shake things loose have you ever tried this ?
you know i saw this one post somewhere where this guy put sand and pebbles in a gas tank sealed it then wrapped in blankets taped it down and threw it in the dryer on tumble dry. it came out clean and no chemicals were needed.
